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Frontispiece 


John-Vaoi Voorst, Londcm 





HUMBLE CREATURES; 

PART I. 

THE EARTHWORM 

AXD 

THE COMMON HOUSEFLY. 


IN EIGHT LETTERS. 

BY 

JAMES SAMUELSON, 

ASSISTED BY 

J. BRAXTON HICKS, M.D. Lond., F.L.S., &c. 

WITH 

MICROSCOPIC ILLUSTRATIONS 

BY THE AUTHOES. 


Centbiasi 2,uv. 


SECOND EDITION. 

LONDON: 

JOHN VAN VOORST, PATERNOSTER ROW. 


MDCCCLX. 


“ The bird that soars on highest v.'ing 
Builds on the ground her lowly nest ; 

And she that doth most sweetly sing, 

Sings in the shade when aU things rest ; — 
In lark and nightingale we see 
\Miat honour hath humility.” 

Montgomery. 


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U' ‘i 

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PRINTED BY TAYIiOR AND FRANCIS, 
RED LION COURT, FLEET STREET. 


TO 


WILLIAM SPENCE, Esq., F.R.S., E.L.S., 

Author of the “ Introduction to Entomology,” &c. 


Dear Sir, 

With your permission the following pages are 
dedicated to you, as a testimony of high esteem and 
respect; and in order to show you that yom‘ oivii 
labours have home fimits in the minds of others, wdio, 
desiring to benefit by your praiseworthy example, have 
devoted a few of their leisure hours to the task of 
investing Natural History with popular interest. 


THE AUTHORS. 


PREFACE TO THE SECOND EDITION. 


In publishing a Second Edition of this little treatise, 
the opportunity has been taken of carefully revising 
the text, and improving the details of the engravings, 
some of which are new. 

In the second part of this Series, in the “ Honey 
Bee,^^ more ample details of the structvire of the 
eyes, antennae, and internal organization of the insect 
races will be found, than have been here presented. 


Liverpool, July 1860. 


iNXnODUCTOBY 


LETTEK I. 


page 1 


LETTER n. 

The Class “ Vermes ” and its subdivision into Orders. — 
Lumbrtcus terrestris, the common Earthworm. — Its Form. 

— Members of Locomotion. — Mouth. — Miment. — Nature 
of Worm-Castings. — Digestive Organs. — Circulating Ap- 
paratus. — ^Nervous System S 

LETTER m. 

Mode of Reproduction in the Earthworm. — Its Habits. — 
Dwelling. — Uses in the Formation of the Surface Soil. — 
Conclusion 17 


LETTER IV. 

Cuvier’s Classification of Annelides and Insects. — Guides to 
a Systematic Arrangement of Animals. — Affinities be- 
tween the Worm and Fly. — Classification of Insecta, and 
the position of the House-fly (Musca domestica) in the 
Class. — General Consideration of the Fly’s Form and 
Structure 26 


LETTER V. 

The Antenna; or Feelers of the Fly ; their Structure ; and 
various theories regarding their Functions. — The Eyes, 
compound and simple ; their Structure and Uses 34 


VI 


CONTENTS. 


LETTER \T. 

The Mouth of Insects. — The Proboscis of the Fly. — The 
Members of Locomotion. — Wings; their Structure. — 
Wonderful Rapidity of Flight. — Halteres or Poisers; 
their Anatomy and supposed Function. — The Legs. — 
Remarkable Organization of the Fly’s Foot. — Repetition 
of similar parts in the organs described page 43 

LETTER VII. 

The Anatomy of the Fly. — Its Organs of Digestion; of 
Circulation ; of Respiration. — Wonderful Structure of the 
Spiracles, or Breathing-holes ; and Trachese, or Respira- 
tory Tubes. — Nervous System. — Considerations upon the 
Nervous System of the House-fly, as compai-ed with that 
of its Larva and of the Worm 64 

LETTER \TII. 

Life-history of the Fly. — Organs of Reproduction. — Mode of 
depositing its Eggs. — Table showing its remarkable Re- 
productive Powers. — The Lan a ; the Pupa ; Transforma- 
tions. — The perfect Fly ; its Habits. — Strange fatal 
Disease to which it is subject. — Its uses as a sanatory 
agent, &c. — Transformation of Matter in the Animal 
Creation. — Reflections upon Geological Facts in con- 
nexion with the Fly. — Conclusion 04 


INDEX TO PLATES. 


Pl. I. Frontispiece. 

Pl. II •page 8 

Fig. 1. Young Worm escaping from pupa-case. 

Fig. 2. Earthworm, showing hooks and swelled rings. 

Fig. 3. Anterior rings of Worm, with lip, hooks, and 
respiratory apertures. — From Burmeister. 

Fig. 4. Transverse section of Worm. — From ditto. 

Pl. ni. Diagram showing the anatomy of Musca vomitoria 26 

Pl. IV 34 

Fig. 1. Head of House-fly, magnified 20 diameters : 
a, a, feelers ; b, h, compound eyes ; c, proboscis. 
Fig. 2. Magnified portion of detached cornea. 


Fig. 3. Section of part of compound eye. 

Fig. 4. Five ocelli, highly magnified. 

Pl. V. Proboscis of House-fly 43 

Fig. 1. Proboscis entire, showing lancets, &c. 

Fig. 2. Magnified ribs. 

Fig. 3. Magnified section of ribs. 

Pl. VI 61 


Fig. 1. Section of Fly, showing nervous system, &c. ; 

a, wing ; b, nervous system. 

Fig. 2. Antenna of Fly. 

Fig. 2 a. Sensory depressions and closed sacs on the 
same, highly magnified. 


Vlll 


INDEX TO PLATES. 


Fig. 3. One of the holteres. 

Fig. 3 a, b. Vesicles at the base of the same, highly 
magnified. 

Fig. 4. Leg of Fly : a, coxa ; b, trochanter ; c, femur ; 
e, tibia ; /, tarsus. 

Fig. 6. Trachea, or respiratory tube, with coil. 

Pl. VII page 64 

Fig. 1. Last joint of tarsus, or foot of Fly, wth hooks 
and pads. 

Fig. 1 a. Portion of fringe, magnified 900 diameters, to 
show the supposed suckers. 

Fig. 2. One of the stigmata or breathing-apertures, 
shown by transmitted light. 

Pl. VIII. (Figures after Griffith.') 04 

Fig. 1. Larva of House-fly (natural size). 

Fig. 1 a. The same (magnified). 

Fig. 2. Pupa (natural size). 

Fig. 3. Lid of pupa-case (magnified). 

Fig. 4. Anterior extremity of larva, showing hooks 
(magnified). 

Fig. 6. Anterior extremity of larva, with palps retracted. 

Fig. 6. i\nterior extremity of larva, with the same ex- 
panded, showing also the trachea and rudi- 
mentary feet. 


THE EARTHWOEM 


AXD 

THE COMMON HOUSEFLY. 


^ 

LETTER I. 

INTRODUCTORY. 


Reader, 

From the title of this Treatise you will see that we 
invite you to consider with us the natural history of 
two creatures which are usually supposed to rank 
amongst the humblest in the Animal Kingdom, and 
which, although exceedingly familiar to us, are, com- 
paratively speaking, less understood and appreciated 
than almost any other living forms. But why should 
this be the case ? Suppose any one were to inquire 
of us whether we are aware upon what principle, and 
of what materials, a penknife, or any ordinary article 
in daily use is constructed, and to what purposes it is 
applied, we should hardly thank him for his estimate 
of our knowledge with regard to common things; 
but we should feel in no way affronted, if, instead, he 
asked us whether we possessed similar information 


B 


2 


HUMBLE CREATURES. 


respecting the worm or the fly, as to how they are 
formed, for what useful ends they have been created, 
and what place they occupy in the realms of Nature; — 
as though the M'orks of man were entitled to a prior 
place in our thoughts to those of our Creator ! 

Not only, however, do these humble creatures 
merit our attention on the ground that they rank 
amongst the valuable works of Nature, but also as 
affording useful lessons in the education of our 
minds ; for unless we carefully examine and endea- 
vour to comprehend the character and attributes of 
the lower animals, we remain children in the know- 
ledge of Nature. 

The rich coat of the leopard, the beautiful and 
variegated plumage of the bird of paradise, the sweet 
note of the nightingale, and the graceful form and 
movements of the gazelle, all delight the senses, but 
tend little towards the elevation of the intellect. 
These afford gratification alike to the savage, the 
child, and the educated man — perhaps in a less degree 
to the last than to either of the former ; but when we 
come to examine those creatures that offer no such 
attractions to the superficial obsen^er, we find them 
to be so wisely constituted, and to possess such in- 
teresting appliances by wliich they perform their 
natm’al functions, that we begin to wonder how it is 
we should have remained so long in ignorance of 
their remarkable properties. We find oiu’selves in a 
new world, and the objects contained therein, at the 
same time that they impart sensations quite as plea- 


INTRODrCTORY. 


3 


surable as those which were wont to excite our childish 
imaginations when first we heheld the more beautiful 
of the higher animals, communicate new ideas; a 
fresh capacity to imitate and design ; and, what is of 
far greater importance, they instil into our minds 
careful habits of observation, and enable us to form a 
more correct estimate of our own humble capacities, 
and of the boundless power and wisdom of our Creator. 

But whilst w'e regard this study as an element in 
the education of our intellect, let us not omit to 
mention, that the pleasurable sensations to which we 
have alluded, as arising from the investigation of 
those objects of which it treats; objects that are 
within the reach of every one ; also render it a de- 
lightful recreation, — ay, we can unhesitatingly say, 
the most effective mode of relaxation for those whose 
days are passed, and w'hose minds are occupied, in 
the oppressive cares of business. 

The formal pages of this book, with its imperfect 
illustrations, will enable you to form but a faint idea 
of the attractions which are presented by such a 
pursuit ; but you have only to inquire of some zealous 
entomologist, microscopist, or other natural student, 
to hear how many delightful hours he has spent in 
the green fields, or in country lanes searching for 
objects, and how many agreeable evenings have been 
passed in their investigation. He w’iU not fail to 
comdnce you that there is considerable enjoyment 
connected with the study. 

Or, if you are not satisfied with the ipse diwit of 

B 2 


4 


HUMBLE CREATURES. 


another, \vho may appear to you an imaginative enthu- 
siast, let us ask you to try the experiment yourself, 
and form your own opinion on the subject. 

The next time you go out on your morning or 
evening ramble, if yon chance to see a worm in your 
path, do not kick it aside, nor step over it ; but take 
it from the ground, and lay it on the palm of your 
hand ; and as it tries to crawl away you will experi- 
ence a slight sensation of roughness on your skin. 
If you take a pocket-lens, and examine carefully the 
under side of the worm’s body, you will perceive 
several rows of fine sharp hooks, extending from one 
end to the otlier, each annulated division (for the 
worm’s body is, as you doubtless know, composed of 
rings) being furnished with four pairs of these hooks, 
which are situated upon small protuberances on the 
creature’s skin. These minute hooks cause the rough 
sensation alluded to; and that portion of the body 
on which they are placed corresponds to the abdomen 
of the higher animals, the hooks themselves being 
nothing more nor less than rudimentary feet to aid 
the worm in its progress (PI. II. fig. 2). 

It has perhaps never occurred to you to inquire 
how it is, when vou endeavour to draw a worm forth 
from the earth, that it can offer such resistance to 
your efforts, as almost to necessitate your tearing it 
in two before you can extract it, and why, as soon as 
you relax your hold, it disappear with such rapidity 
under the soil. These hooks are the cause ; they are 
retractile at the will of the animal, and operate so as 


INTRODUCTORY. 


not to impede its onward progress : but when a portion 
of its body is once extended, and has penetrated into 
the soil, they keep it firmly fixed, whilst the remain- 
ing part is drawn after it by muscular contraction. 

Now, is not this a simple but interesting feature in 
the anatomy of the worm, that should be known to 
every one ? — yet how few, even of the best educated, 
are aware of its existence ! How many anglers, do 
you think, are there, who handle their poor victim as 
frequently as Ave do our pen, and are yet unacquainted 
with this fact ! 

And as regards the Fly ; you need not even quit 
your study or parlour to have an opportunity of Avit- 
nessing a strange, and, to the masses, inexplicable 
phenomenon connected with the insect, namely the 
mode in which it Avalks upon the ceiling Avith its feet 
upwards, or progresses upon the smooth vertical pane 
of glass in your parlour AAundow, setting at defiance a 
Avell-known laAV of gravitation. If you are not able 
to solve this mystery, ask some friend who possesses 
a microscope to sIioav you the foot of a fly under the 
instrument, and you Avill find, that at its extremity it 
is furnished Avith a pair of membranous discs, on 
Avhich there are disposed countless minute suckers, 
that operate upon the inverted ceiling, or smooth 
glazed surface over Avhich the fly is marching, in the 
same manner as did tlie leather sucker with Avhich, as 
a schoolboy, you Avere wont to amnse yourself in 
lifting hcaA'y stones : this is the simple, but effective 
apparatus Avhich enables the little creature to main- 


6 


HUMBLE CREATURES. 


tain its hold with security in any position (PI. VII. 
figs. 1 & 1 c). 

Nay, you may even, whilst lounging lazily upon 
your sofa, w^atch some little fly that has settled upon 
your coat, and is busily engaged in remo\dng the dust 
from its wings : you wiU notice with what facility it 
crosses its hinder legs over the wings, or raises the 
latter gently from beneath ; and after having effected 
this cleansing operation, then rubs one leg against 
the other, to remove any particles of dust from these 
members also. But are you aware that for this pur- 
pose its diminutive limbs are covered with numberless 
hairs, by means of which the insect is enabled as 
efficiently to remove the dust from its wings or body, 
as you are from your treasured volumes or pictures 
with your artificial brush of similar materials ? 

These are two of the numerous evidences revealed, 
to us when we examine the Fly’s structure, of the care 
wdth which the insect has been endowed with organs 
that conform perfectly to its mode of existence; 
showing, that however useless and unimportant it 
may appear to us, and although we may regard it as 
a plague in our dwellings, yet every provision has 
been made for its comfort and safety. 

Let us adduce one still more remarkable and in- 
teresting example : — 

Whilst we possess only two eyes, beautiful and 
perfect, no doubt, in their construction, the humble 
Fly is furnished with about 4000 simple, but perfect 
organs of vision ; and even this number falls far short 


INTRODUCTORY. 7 

of that in other insects. Many have been the con- 
jectures why the insect races are thus liberally, in- 
deed to all appearance lavishly, supplied with visual 
organs. We shall detail their nature and probable 
operation further on ; but may here observe, that, so 
far as we are able to judge, they are the best adapted 
to the habits of the insect ; and that the end required, 
namely the conveyance to the brain of a distinct 
image of surrounding objects, could not have been so 
effectually attained by any other contrivance. 

We trust that these brief allusions to a few of the 
most striking phenomena connected with the exter- 
nal stmcture of the Avorm and the fly, may have 
aAvakened in your mind some curiosity to know more 
of these household forms ; or will at least have satisfied 
you that they are wonderfully constructed for wise 
and good piuqioses ; and Ave hope that you may noAV 
be induced to pass on with us to a nearer consider- 
ation of their structure and habits. 

We shall endeavour, as concisely as possible, and 
so far as it lies in our poAver, to make you acquainted 
Avith the present state of knowledge regarding their 
natural history ; but, as a great deal that relates to 
their various organs has still to be elucidated, we 
shall append, in notes, the names of the various 
authors Avho have devoted their attention to the sub- 
ject, and of such of their Avorks as Ave have employed 
as reference, in order that you may, if so inclined, 
avail yourself of these pages merely as a guide to a 
more comprehensive vicAv of the subject. 


8 


HUMBLE CREATURES. 


LETTER II. 

THE CLASS VERMES AND ITS SUBDIVISION INTO ORDERS. — 
LUMBRICUS TERRESTRI8, THE COMMON EARTHNVOHM. — ITS 
FORM. — ^MEMBERS OF LOCOMOTION. — MOUTH. — ALIMENT. — 
NATURE OF WORM-CASTINGS. — DIGESTIVE ORGANS. — CIRCU- 
LATING APPARATUS. — NERVOUS SYSTEM. 

Few persons have a eorrect idea of the extent of that 
group of animals known as the Vermes” or Worms. 

Many, whose acquaintance with zoology is very 
limited, believe the use of the term to be restricted 
to the Earthworm, and intestinal worms, such as the 
Tapeworm, and the Ascarides, or small round worm 
of infants; others again, although aware that these 
creatures do not alone constitute the class, know 
little of the remaining forms Avhich it contains. Let 
us therefore, whilst treating of this portion of the 
subject, endeavour to form some general idea of the 
whole class, and inquire what are its distinguishing 
characteristics. 

The “Vermes,” which occupy a distinct position 
in the Animal Kingdom, have soft elongated bodies, 
possessing neither an internal skeleton, as we find 
in the vertebrated animals, nor (as a general rule) 


Plate VII 


I 



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P>^3 


Fi|4. 





J oamuclffon del 


U H KivvL ijtii 


.John Van Voorst, -Landau 


CLASS VERMES. 


9 


external hardened eases, as in the beetle and other 
inseet tribes; nor yet a caleareous shell, as in the 
univalve or bivalve moUusks, sueh as the snail 
and oyster. With few exeeptions, their bodies are 
unprotected by any kind of hai’dened envelope, and 
they possess no ai*ticulated members of locomotion. 
They are usually enclosed in a tough skin, and their 
bodies are composed of a series of segments, all of 
which, with the exception of the first, which repre- 
sents the head, resemble each other in almost every 
respect. 

Some of the most recent and accurate writers on 
zoology have divided the whole class into four orders, 
possessing distinct and well-marked peculiarities*. 

1. The lowest of these is that of the Nematoid or 
round w'orms, whose bodies are not annulated, nor 
divided into distinct sections, but present an almost 
unbroken cylindrical form. These are for the most 
part intestinal worms ; and theAscaris and Strongylm, 
the former inhabiting the intestines of man, the 
latter an enormous, usually fatal worm found in the 
kidney of the pig, may serve as examples of the 
order. 

2. The next division, that of the Platyehnia, or 
flat worms, is more numerous than the last. In some 
cases, as in the Cestoid worms (e. g. the Tania, or 

* Vogt, Zoologische Briefe. Frankfort, 18i51. — Cai-penter, 
The Microscope. London, 1850. — See also Burmeister’s Zoolo- 
gical Atlas. Berlin, 1843. — Achille llichard Elements dTIi- 
stoire naturelle. Pari.s, 1849. 

B 5 


10 


HUMBLE CREATURES. 


common Tapeworm)^ the body is divided into a great 
number of segments, all similarly formed and or- 
ganized j in othei*s, as in the Ptanarian worms, inha- 
biting the water, it consists of one flattened, undivided 
disc. These are two of the great variety of groups 
and families which comprise the order. 

3. The third order is wholly microscopic. They 
are termed the Rotifera, or wheel-bearing worms, 
are found in incalculable numbers in fresh and salt 
water, and present almost every conceivable form. 
They are distinguished, as their name denotes, by the 
so-called “ wheels,” wreaths of minute hair-like pro- 
cesses termed “ cilia,” situated on the head. These 
cilia are kept in a state of constant vibration, and 
perform the functions of locomotion as well as of 
nutrition. Many of the Rotifera, minute though they 
be, have their bodies protected by beautiful trans- 
parent cases. 

4. The last and highest group is that of the Anne- 
lida, or annulose w'orms, in which is included the sub- 
ject of our remarks, the Earthworm. Also the various 
groups of worms represented by the Leech) the Serpula 
and Terebella, which arc found on the sea-shore, and 
construct for themselves tubular dwellings ; the Nais 
or Mud-worm ; and the “ Errantia” or “ Natantia ” 
{errant, or swimming ivorms), which represent the 
intermediate type between the Worms and the higher 
articulate groups, and strongly resemble the well- 
known Centipedes in appearance; the chief distinction 
being, that whilst the latter are formed for a terres- 


THE EARTHWORM. 


11 


trial existence, the locomotive members and other 
portions of the swimming-worms are constmcted in 
conformity with their marine life*. 

The Annelida, or annulose Avorms, then, the highest 
and most perfect of the four orders, contain amongst 
their number the EarthAvorm {Lumbricus terrestris), 
Avhich, in common Avdth its congeners, possesses, as 
you well know, a soft elongated body. This, in the 
full-grown animal, is usually dmded into from 120 
to 150 rings or segments, which decrease in circum- 
ference as they approach either end, causing the body 
to terminate in what may be called two pointed extre- 
mities, the head and the tail. To the hooks, situated 
upon each ring of the body, Ave have already alluded 
in our Introduction, and these are the only append- 
ages that the Avorm possesses (see section of Worm^s 
body, PI. II. fig. 4). But you AviU perhaps be some- 
Avhat surprised to hear us speak of the ‘‘head^^ of 
a Avorm, for you are accustomed to connect Avith that 
idea a mouth, eyes, nose, and ears, none of which 
are perceptible in the Avorm ; and the first, that is the 
mouth only, being actually present. Although, hoAv- 
ever, the senses of A'ision, smell, and hearing are, so 
far as we haA'e been able to ascertain, denied to this 
humble Annelide, yet we cannot but grant to its 
anterior final ring the title of a head ; for if you exa- 
mine it AvIth a pocket-lens, whilst the creature raises 
that part of its body, you will perceive upon it a 
* See note, page 27, Letter IV. 


12 


HUMBLE CREATURES. 


well-formed protruding upper lip, to which a smaller 
or lower lip is placed in juxtaposition. 

These two lips form an imperfect ring, and consti- 
tute the oral aperture or mouth, which is however 
not provided with teeth, nor organs of any other 
description. This being the case, and as the worm 
possesses no prehensile members udth which to lay 
hold of its food, you will naturally be curious to know 
upon what it subsists, and how it obtains its nourish- 
ment. 

You have doubtless heard of the chameleon, which, 
wonder-loving sages tell us, feeds upon the air*. At 
least you will say, this diet cannot be very indigest- 
ible ; but we fear you will smile incredulously when 
informed that the Earthworm not only inhabits the 
earth, but also feeds upon the element in which it 
exists; and although some naturalists have declared 
that it derives its nutriment from the roots of plants, 
yet this statement, according to the most reliable au- 
thorities, is now pronounced to be a pure fable. The 
soil is, as you will probably be aware, impregnated 
with decaying organic substances of various kinds, 
and in order to secure these for its sustenance, the 
worm gorges itself with earth; the nutritive consti- 
tuents are extracted in its stomach by the digestive 
process, and the indigestible portion ejected in little 

* The chameleon subsists upon small insects, which it is 
enabled to seize by darting forth its wonderfully constructed 
tongue with great rapidity. See Carpenter’s ‘ Zoology.’ Lon- 
don, 1857. 


THE EARTHWORM. 


13 


worm-shaped masses, well known to gardeners and 
others as “ worm-castings.” Of these more hereafter. 

The digestive apparatus is of the simplest kind, 
consisting of a straight alimentary canal which runs 
from one end of the body to the other, commencing 
at the mouth and terminating in the final posterior 
ring. This tubular stomach is slightly constricted at 
each ring, and is covered externally along its wdiole 
length with a granular envelope, composed of nu- 
merous glands, wliich secrete a fluid that aids in the 
digestion of the alimentary substances and their 
elaboration into the blood (PI. II. fig. 4, section of 
Worm’s body, showing the form of alimentary canal). 

If you examine the living -worm, you will notice a 
fine crimson streak shining tlu’ough its semitrans- 
parent covering; this is the main trunk or artery 
which extends along the whole body, in the same 
manner as the alimentary canal, and serves as the 
receptacle of the blood. To observe the circulation 
of the latter, you need but remove a -worm from the 
ground, and keep it a little while, until it has voided 
the earth which it contained, and thus rendered its 
body more transparent ; you will then be able to distin- 
guish the crimson current as it courses along the crea- 
ture’s back, flowing from the tail to the head confined 
within the central artery ; and on turning it upon its 
back you wdll perceive the return current flowing in the 
opposite direction, tlirough another blood-vessel, situ- 
ated near the abdominal surface. The dorsal vessel 
must be regarded as the heart, and partakes to some 


14 


HUMBLE CREATURES. 


e.\teut of the nature of that organ in the liigher ani- 
mals, inasmuch as its wall, or limitary membrane, is 
elastic, and by its contractions propels the blood on- 
wards. hilst thus passing along the main artery 
it is brought into communication with the atmo- 
spheric air, to be renewed by the absorption of oxygen, 
in a manner which we shall presently describe ; and 
then returns, as already explained, along the second 
(abdominal) canal, which is miited to the former by a 
number of smaller veins into winch the blood also 
penetrates, so that it may yield its regenerating con- 
stituents to every portion of the body. 

The aeration of the blood takes place as follows : — 
On closely examining the dorsal surface of the worm 
with a pocket-lens, a minute circular aperture is 
distinguishable between each ring and the adjoining 
one (PI. II. fig. 3). By these the air is admitted into 
the body, and being conducted by special canals to 
the dorsal circulating organ, there gives off its oxygen 
to the contained fluid. 

So far, then, we find that the nutritive organs of 
the worm resemble in principle those of the higher 
animals ; for although it possesses no central organs, 
such as the stomach and heart, yet, in the alimentary 
system, the intestine or canal, with its glands, per- 
form the functions of the former, whilst the place of 
the heart is supplied in the circulating system by the 
contractile dorsal vessel. As, however, these organs 
are more highly developed in the Fly, the physiology 
of which w'e shall consider in a subsequent letter, we 


THE EARTHWORM. 


15 


have made but brief allusion to them here, and wdll 
now conclude this letter with a few w'ords in regard 
to the nervous system of the Earthworm. 

This is Iramed in conformity with the general shape 
of its body^ and is as simple as the organs already 
described. It consists, firet, of a minute roundish 
mass of nervous substance, termed the “cephalic 
ganglion,” wliich corresponds to our brain, and is 
composed of two smaller masses, of equal size, fused 
together. The “ cephalic ganglion” is situated in the 
head, just above the tlnoat (if the commencement of 
the long alimentary canal may be so termed), and 
from each of its hemispheres there proceeds a nervous 
chord, one of which passes downwards and backwards 
on either side of the throat, and the two again amal- 
gamate under the alimentary canal. Hence they are 
continued, as a single nervous stem, along the whole 
ventral portion of the body, close to the external sur- 
face, giving out in each ring a number of branches of 
remarkable delicacy, which encircle the body, passing 
round to the creature’s back, and imparting sensi- 
bility to every portion of its frame. (See ! what excni- 
ciating pain the angler mflicts upon the poor worm 
when he impales it upon his barbed hook, which he 
passes from one end of its body to the other !) 

Even in this apparently uninteresting part of the 
animal’s structure a noteworthy trait presents itself, 
namely, that whilst in our bodies, and those of the 
vertebrate animals generally, the spinal chord passes 
along the back-, in the worm, and, let us add, in all 


16 


HUMBLE CREATURES. 


the articulate races — wonns, millipedesj crustaceans, 
arachnidse, and insects, — -the central nerv'ous stem 
traverses the opposite, that is, the ventral side, almost 
immediately in contact with the outer surface. 

There now remain to be considered, in connexion 
with the natural history of the Earthworm, its organs 
and mode of reproduction, and also its habits of life, 
and obvious uses. 


THE EARTHWORM. 


17 


LETTER in. 

MODE OP REPnODUCTION IN THE EARTHWORM. — ITS HABITS. 

— DWELLING. — USES IN THE FORMATION OP THE SURFACE- 

SOIL. — CONCLUSION. 

In out last letter we reviewed eursorily the ehief por- 
tions of the AYorm’s anatomy, and must now devote 
a short spaee to the consideration of its organs and 
mode of reproduction. 

The worm, in common with many others of tlie 
humbler animals, is remarkably endowed in this 
respect, each creature possessing within itself both 
the male and female organs of reproduction. These 
strongly resemble each other in appearance, for both 
consist of a series of what physiologists term “ tubuli,” 
or little tubes, one set of ivhich serv'es for maturing 
the female ova, and the other for the development of 
the male spermatozoa, little motile fructifying bodies 
visible only under the microscope. 

At certain seasons of the year, when the ova are 
ripe, and ready for fecundation, a number of the 
rings, usually from four to eight (PI. II. fig. 2), 
situated at about the anterior third of the body, be- 
come eidarged, and this swelling, which you will 


18 


HUMBLE CREATURES. 


doubtless often have notieed, strongly resembles a 
healing wound, for whieli it is usually mistaken by 
the uninitiated. From this portion of the body a 
glutinous substanee, secreted by special glands, ex- 
udes; and although, as just observed, the worm is 
hermaphrodite, yet contact "with another of its species 
being necessaiy for fecundation, the creature leaves 
its underground haunts at night, and, coming to the 
surface, adheres by its swelled and glutinous rings to 
the same rings upon the body of another worm. 
Through this act, the ova and spermatozoa are libe- 
rated in each worm from the respective tubuli in 
which they were contained, and pass into the general 
cavity of the body ; they there encounter each other, 
and fructification of the ova is the result. A great 
deal, however, remains unexplained concerning the 
reproductive process in the Earthworm, as well as in 
regard to the development of its young. 

Respecting the latter, we know that the young 
worm is usually developed whilst still in the ovum 
within the parent’s body; and, what is somewhat 
strange, it is sometimes born naked, whilst at others 
it is enveloped in a hard covering, which subsequently 
bursts, and allows the young worm to escape (PI. II. 
fig. I). This difference in the stages of development 
when the worm leaves its parent, depends,” we are 
told, “ on the nature of the soil which the worms are 
inhabiting : in a light and loose soil, the young quit 
the parent prepared to act for themselves ; but in a 
tough clayey soil, they continue in the pupal form for 


THE EARTHWORM. 


19 


some time, so as to arrive at a still higher degree of 
development before commencing to maintain an in- 
dependent existence*.” 

Although, however, the young worm is bom in the 
fully-developed shape of its parent, yet, as it increases 
in size, the number of its rings is augmented by the 
subdivision of those which it possessed at its birth, — 
a circumstance that denotes its humble position in 
the animal scale ; for the lower we descend, the more 
frequently we find living forms endowed with the 
power to reproduce, by a vegetative process, similarly 
organized portions of their frame after they have left 
the body of the parent. Notwithstanding, however, 
that the worm occupies so humble a position, you 
Mull have seen, from the preceding outline of its ana- 
tomy, that no essential parts of its structure are want- 
ing, and that, like all other created beings, it is per- 
fect, so far as regards adaptation to its mode of ex- 
istence. It is not indeed furnished (according to our 
present knowledge) with any of those more delicate 
organs of sense that characterize the higher animals ; 
but then, of what service would eyes and ears be to a 
creature which we know spends the greater portion of 
its existence undergroimd ? Its dwelling consists of 
one or more bun'ows, of the same shape as its body, 
which it constmets beneath the surface, and lines 
with a kind of slime, so as to render the walls con- 
sistent, and thus prevent the soil from falling in and 
closing up the cavity. These burrows it quits when 
* Carpenter’s ‘ Comparative Physiology,’ p. 693. 


20 


HUMBLE CREATURES. 


compelled to do so by the spade of the labourer — 
(and the worm is said to be very sensitive to any dis- 
turbance of the soil in its vicinity), — when it wishes 
to visit the surface in search of a mate, or in order to 
discharge from its body the earth from which it has 
extracted the decaying organized matter by the di- 
gestive process. In this last operation it performs an 
act of great utility to the agriculturist, inasmuch as 
it enriches the surface soil by the deposition of those 
little heaps of earth which Ave alluded to in a former 
letter under the designation of ‘^worm-castings.” 
We shall narrate briefly how this interesting circum- 
stance was first discovered, shoAving at the same time 
hoAv important a part the Avorin plays in the con- 
struction and fertilization of the soil. 

About tAventy years since, an eminent naturalist*, 
Avhilst visiting a friend in the country, Avas surprised 
to hear from his host, that on some pasture-lmidi 
Avhich he possessed, an unaccountable change had 
taken place in the character of the soil, which in 
various fields had, Avithout apparent cause, materially 
increased in depth diuring the preAuous years, and 
that cinders and other substances, Avhich had ori- 
ginally been thrown upon the surface, had apparently 
sunk to a considerable depth in the soil. Curiosity 
induced him to try a few experiments in order to 
ascertain the cause of this strange phenomenon, and 
with this view he dug several holes in different fields ; 

• Mr. Darwin. See ‘ Transactions of the Geological Society,’ 
2 ser. vol. v. p. 605 ; his paper “ On the Formation of Mould.” 


THE EARTHWORM. 


21 


in these he found similar indieations of a gradually 
increasing thickness in the surface-soil, and beneath, 
an accumulation of pebbles, cinders and lime, which 
had originally been deposited on the surface. In one 
field, for instance, the cinders which had been thrown 
on the surface three years previously, were buried to 
the depth of an inch; in another they were buried 
three inches deep, and formed a layer an inch in 
thickness. But let us give the narrative in his own 
words : — 

“ The appearance in all the above cases was as if 
(in tbe language of farmers who are acquainted \nth 
these facts) the fragments had ‘ worked themselves 
down.^ It is, hoflxver, scarcely possible that cinders 
or pebbles, and still less powdered quicklime, could 
sink througb compact earth and a layer of matted 
roots of vegetables, to a depth of some inches. The 
explanation of these facts which occurred to Mr. 
Wedgewood’^ (his host), “though it may appear trivial 
at first, I have no doubt is the correct one, namely 
that the whole operation is due to the digestive pro- 
cess in the common Earthworm. On carefully exa- 
mining between tbe blades of grass in the fields above 
described, I found scarcely a space of two inches 
square Muthout a little heap of cylindrical castings of 
worms. It is well known that worms in their exca- 
vations swallow earthy matter, and that, having sepa- 
rated the portion which serves for their nutriment, 
they eject at the mouth of their burrows the remainder 
in little intestine- shaped heaps. These partly retain 


22 


HUMBLE CREATURES. 


tlieir form imtil the rain and thaws of winter spread 
the matter uniformly over the surface. The worm is 
unable to swallow coarse particles, and as it would 
naturally avoid pure or caustic lime, the finer earth 
lying beneath the cinders, burnt marl or lime, would 
be removed by a slow process to the surface. This 
supposition is not imaginary, for in the field in which 
the cinders had been spread out only half a year 
before, I actually saw the castings of the worms 
heaped on the smaller fragments. Nor, I repeat, is 
the agency so trivial as at first it might be thought, 
the great number of earthworms, as every one must 
be aware who has ever dug in a grass-field, making up 
for the insignificant quantity of the work which each 
performs. 

“ On the idea of the superficial mould having been 
thus prepared, the advantage of old pasture-land, 
which, it is well known, farmers in England are par- 
ticularly avei*se to break up, is explained, for the 
length of time required to form a thick stratum must 
be considerable. In the peaty field, in the course of 
fifteen years, about 3^ inches had been well pre- 
pared; but it is probable that the process is con- 
tinued, though at a very slow rate, to a much greater 
depth. Every time a worm is driven, by dry weather 
or any other cause, to descend deep, it must bring to 
the surface, when it empties the contents of its body, 
a few particles of fresh earth. Thus the manures 
added by man, as Avell as the constituent parts of the 
soil, become thoroughly mingled, and a nearly homo- 


THE EARTHWORM. 


23 


geneous character is given to the soil. Although the 
eonclusion may appear at first startling, it avlII be 
difficult to deny the probability, that every particle of 
earth, forming the bed from which the turf in old 
pasture- land springs, has passed through the intes- 
tines of worms, and hence the term ‘ animal mould ’ 
would in some respects be more appropriate than that 
of ‘ vegetable mould.’ ” He eoncludes by remarking, 
“ that the agriculturist, in ploughing the groimd, 
follows a method strictly natural ; he only imitates 
in a rude manner, without being able either to bury 
the pebbles, or to sift the fine from the coarse earth, 
the work which Nature is daily performing by the 
agency of the Earthworm.” 

With regard to the latter portion of these remarks, 
exemplifying, as they do, in a forcible manner the 
prineiple to whieh we have more than once alluded 
in the eourse of this short history, namely that 
Nature has not bestowed all these pains on the for- 
mation of the worm without some useful end, we 
would now also add a few Avords in concluding this 
section of our treatise. 

Those who know what astonishing results are pro- 
duced by the labours of the minute and (compared 
with the Avorm) still more humble Madrepore polyp, 
eommonly knoAvn as the Coral insect; how in the 
course of ages it bulds up continents in the midst of 
the ocean ; Avill not for an instant be inclined to doubt 
that the worm aids in the deposition of the suiTace- 
soil, simply on the score of its apparent insignifi- 


24 


HUMBLE CREATURES. 


cancc; and although the traces of the Annelicle in 
the geological formations of past ages are but slight, 
yet it is believed by reflecting observers that the 
little creature has (as in the case of the poh^p just 
referred to) pui’sued its labours from a very early 
period in the earth’s history. 

But be that as it may ; suppose its operations have 
only been confined to the deposition of a portion of 
the existing moidd, a circumstance which we believe 
to be placed beyond a doubt ; still oiir assertion holds 
good, that its history afibrds a striking exemplifica- 
tion of the divine truth, that no creature has been 
formed without its special ends, and that the humblest 
are frequently selected to carry out the most gigantic 
natural operations. And again, what can be more 
obvious, than that the Earthworm, by aiding in the 
accumulation and fertilization of the surface-soil on 
pasture-lands, is the indirect means of supplying us 
with many of our most valuable comforts and luxuries ; 
that the verdant meadows which clothe the surface of 
the earth in a robe of evergreen, and afibrd nourish- 
ment to the herds of cattle that have been bestowed 
upon man as his birthright, are rendered still more 
verdant and fruitful by its untiring labours ? There 
it toils away, unconscious of its great mission, again 
and again penetrating the earth, and each time, when 
it returns to the surface, bringing up wdth it a small 
portion from below to aid in the restoration of the 
exhausted soil, and multiply the comforts of the 
human race. 


THE EARTHWORM. 


25 


At length, if it be not hunted by some angler, and 
prematurely tortured to death, to assist liim in his 
sport as a requital for the sendees it has rendered to 
his race, it concludes the chapter of its usefulness by 
serving as wholesome nourishment for one of the 
winged inhabitants of the air. 

Reader ! this is the story of the Worm’s life. 


c 


26 


HUMBLE CREATURES. 


LETTER IV. 

cuvif.b’s classification of anneltdes and insects. — 

GUIDES TO A SYSTEMATIC ARRANGEMENT OF ANIMALS. — 
affinities between the worm and fly. — CLASSIFICATION 
OF INSECTA, AND THE POSITION OF THE HOUSE-FLY (mUSCA 
DOMESTICA) in THE CLASS. — GENERAL CONSIDERATION OF 
THE ply’s form AND STRUCTURE. 

On referring to Cuvier’s classification of animals, you 
will find that, according to the views of that great 
zoologist, the Annelides should be included amongst 
the Articulata (articulate races), and that he regards 
them as the lowest, and the Insecta, or Insects, as the 
highest class in that section of the Animal Kingdom. 
Now, although in treating of the Earthworm, which 
you of course know to be one of the Annelida, we 
place that group at the head of the Class Vermes, in 
conformity with the arrangement of the most recent 
and accurate zoologists, yet it is necessary to add, 
that the line of demarcation between the Annulose 
worms and some of the family of Articulata is so faint 
and ill-defined, that many naturalists still continue to 
follow the classification of Cuvier, and consider the 
former as the lowest of the Articulate types. 

It would be advisable, for the better comprehension 


Plate III 



J Sanmglsoii del 


G^Ford }uli 


John. Van Voorst, LonJm 



THE FLY. 


27 


of our subject, that we should inquire what principle 
has of late guided zoologists in their systematic ar- 
rangement of these forms ; and it will then also be- 
come obvious what reason has induced us to couple 
together in this little treatise two such apparently 
opposite creatures as the Worm and the House-Fly, 
employing the first as an introduction to the more 
complicated structure of the second*. 

Those who have acquired at aU a scientific know- 
ledge of zoologj', are well aware that each gi-eat divi- 
sion of the Animal Kingdon exhibits a progressive 
development in the organization of the various groups 
that it contains ; and also, that in following the life- 
history of a single individual in that section, a re- 
markable analogy is apparent between the various 
stages of development through which it passes, and 
those to which we have just referred as existing in 

* In glancing over a Synopsis of the Hunterian Lectures on 
the anatomy and classification of the Invertebrate animals, 
delivered last year by Professor George Busk, F.R.S., at the 
Royal College of Surgeons, we find the relation between the 
Worm and the Fly denoted in a striking manner by the classi- 
fication which that physiologist has adopted. 

Under the title of “ jVnnidosa,” or annulated animals, he in- 
cludes every creature possessing a body composed of rings or 
segments, and amongst the subdivisions of that great class we 
find that he xmites the Amielidcs (of which the Earthworm is 
the tyq)ical representative) to the Insecta, whereof the Fly is 
one of the characteristic forms, by the Myriapoda (Centipedes), 
which partake of the nature of both groups. 

We have seen no classification that confirms so clearly as 
this, the idea wliich induced us to couple the Worm and the 
Fly in one treatise. — (See page 10, Letter II. “ Natantia.’’) 

c 2 


28 


HUMBLE CREATURES. 


the whole class. So striking is this comparative pro- 
gress in the organization of classes and individuals, 
that the lowest creatures in any particular section 
strongly resemble, when in their perfect form, the 
early or embryonic stage of the higher animals in the 
same section, the latter undergoing various changes 
of form and structm’e before they assume their cha- 
racteristic type. 

Let us take, for example, the two groups of which 
we are here treating, namely the AnneUdes and In- 
sects ; the first as having been placed by Cuvier and 
others at the base, the second as the head of the 
Articulate division of the Animal Kingdom; and let 
us also select at the same time, the Worm as the 
typical representative of the former, and the Fly as 
that of the latter group. 

The Annelides have a long, soft, cylindrical body, 
divided into rings, and famished with no external 
members except the rows of hooks that sen’^e to aid 
them in locomotion ; hut as we rise in the scale of 
Articulate animals, their bodies become shorter, and 
are divided into distinct segments irrespective of the 
rings, which decrease in number. The members of 
locomotion are more prominent : first, legs appear, 
which enable the creatures to crawl or leap ; and then 
we arrive at the perfect insect, whose wings, super- 
added to the legs of the lower races, impart to it also 
the power of flight. 

And now as regards the individual. The larva of 
the Fly, or the form in which it leaves the egg, closely 


THE FLY. 


29 


resembles a worm, not only in its external shape, but 
also in its internal physiology ; it possesses loco- 
motive hooks similar to those of the Worm, but not 
so numerous, and more perfectly developed, and its 
elongated cylindrical body is divided into rings only. 
(The points of dijference between the two creatures 
will be noticed hereafter.) When it has passed a 
certain length of time in this stage, it assumes the 
pupa form, being enclosed in a hard fusiform case, 
perfectly motionless, and to all appearance inanimate. 
Whilst in this state, the remarkable change from one 
of the lowest to one of the highest examples of the 
Articulate type is going on ; first the leys and then 
the wings becoming developed ; and when the meta- 
morphosis is complete, the insect bm’sts its prison- 
house and issues forth in its perfect or ' imago ’ form, 
furnished with legs and wings, and all those Avonder- 
ful appliances, Avhich we shall presently describe in 
detail. 

The foregoing comparison will shoAv you, that not 
only the outAvard fonns of animals, but also their life- 
history, and the metamorphoses to Avhich they are 
subject, arc all duly considered by scientific zoo- 
logists, in their systematic classification. But the 
knoAvledge of this fact is aU that need be deemed 
essential for our purpose ; for Ave are not dealing Avith 
groups, nor even genera, but only Avith species ; and it 
matters very little to us Avhether zoologists have 
placed the EarthAvorm at the head of one group, of 
Avhich it is a perfect representative, or at the base of 


30 


HUMBLE CREATURES. 


another, to which it is allied by less powerful links. 
In treating of it jser se, we placed it in the former 
position, denoted by its most important properties. 
And here we draw your attention to its affinities to 
that higher type which we are now about to consider. 

The Class Insecta, to which the House-fly belongs, 
is one of the most extensive in the Animal Kingdom, 
and is divided into several Orders, distinguished from 
each other by well-defined characteristics. The chief 
typical feature of the whole class is the invariable 
possession of six legs by the fuUy developed insect 
{imago), although in the lan^al stage the number of 
these members is arbitrary, varyiug in the different 
groups; and even in some cases they are entirely 
absent. Another, although not so constant an attii- 
bute as the former, is the presence of wings, — ^mem- 
bers that are found in no other group of the inverte- 
brate animals ; and lastly, we may name, as a special 
but not invariable distinction, the division of the body 
into thi’ee sections (hence the term ‘insect^), — head, 
thorax or chest, and abdomen. 

Vogt, whose classification we adopted in our brief 
notice of the Class Vermes, divides the Insecta into 
three great subclasses, characterized by the various 
degrees of metamorphosis that they imdergo before 
arriving at the perfect state. The forms contained in 
the lowest of these subclasses [Ametabola) are subject 
to no important change in their outward appearance, 
excepting so far as their growth is concerned, from 
the time of quitting the egg to the attainment of 


THE FLY. 


31 


maturity. Of this group, which is but limited, the 
Louse {Pediculm) is a w'ell-known, but not very 
agreeable example, and, in common with the other 
genera that constitute this subclass, the Louse is 
apterous, or wingless. 

The second group [Hemi-metabola) undergoes one 
metamorphosis, namely from the larval to the imago, 
or perfect form; their appearance, however, in the 
first of these stages varies but little from that of the 
full-grown insect, the principal distinction being, that 
the wings are wanting in the larva, and only make 
their appearance at a later period of the insect’s ex- 
istence. This group is far more numerous than the 
last ; and as familiar examples, we may quote the 
Earwig (Forficula), the Locust {AcHdium), the Dragon- 
fly (Libellula), and that terror of all good housewives, 
the Bug {Cimex ) . 

Lastly, we have an extensive race of insects that 
undergo a complete transformation {Holometabold) , or, 
more correctly speaking, two changes ; the first from 
larva to pupa, the second from pupa to imago. These 
three stages of growth are so familiar to aU who have 
any knowledge of natural history, that we need but 
allude to the metamorphosis of the Butterfly, first from 
the caterpillar to the chrysalis, and from the latter to 
the winged insect, by way of passing illustration. The 
Bee {Apis), the Wasp {Vesj)a), the ButteiHy {Papilio), 
the Beetle tribes (Coleoptera), and, amongst many 
other similar forms, the common House-fly {Musca do- 
mes tica), are all members of this extensive gi’oup. 


32 


HUMBLE CREATURES. 


Our little Fly, then, belongs to the highest of the 
three subclasses of insects, inasmuch as it undergoes 
a perfect transformation ; and, not to weary you with 
any lengthened reference to orders and genera, we 
will simply add, that on account of its possessing 
two wings, it is included in the Order Diptera, in 
contradistinction to those tribes which are wingless 
{Aptera), and other Orders characterized by the varied 
nature of their organs of flight. 

Having thus cursorily surveyed this proHnce of the 
Animal Kingdom in order to ascertain what rank and 
position are held by the Fly, let us now direct your 
attention to the details of its structure ; and in in- 
troducing this portion of the subject we will first 
observe, that, simple and imassuming as its form may 
appear to the superficial observer, it has been deemed 
worthy of a large share of the zoologists notice j for 
its external members, as well as its internal organiza- 
tion, have been almost as carefully scrutinized and 
accurately described as those of man. 

If you examine the body of a Fly, you will find it 
to be composed of the three sections already refeiTed 
to : the head ; the thorax or chest, joined to the head 
by a thin neck ; and the abdomen. See Frontispiece 
and Plate III. 

Let us examine each division seriatim. 

I. The head bears externally the organs of sense 
and nutrition, that is to say, the antennae or feelers, 
the wonderful eyes (compound and simple), and the 
proboscis j within, it encloses the cerebral ganglion 


THE FLY. 


33 


or brain, and the nen^es of sense proceeding there- 
from to tlie organs just named. 

2. The thorax, or chest, is again subdivided into 
tluee parts; — imperfect rings, the anterior of which 
is termed the prothorax, the middle the mesothorax, 
and the posterior the metathorax. On these tliree 
riims the members of locomotion are distributed as 

O 

follows : viz. on the prothorax is found the first pair 
of legs only ; on the middle or mesothorax, which in 
the Fly is largely developed, the second pair of legs 
and the pair of wings (for, as before remarked, the 
Fly possesses but one pair) ; and on the metathorax 
the last pair of legs, and two organs, termed the 
halteres or poisers ; — the last-named will be fully 
described hereafter. Within the thorax is situated 
the continuation of the nervous system (which here 
consists of the nervous chord, the thoracic ganglion 
and nerves branching from it to the members ; see 
PI. I. fig. 1) ; also the stomach and part of the circu- 
lating and respiratory apparatus. 

3. The abdomen, which bears no external mem- 
bers, is also composed of several rings, and contains 
the intestinal canal, with its appendages ; two pul- 
monary sacs, with other portions of the respiratory 
apparatus ; the many-chambered heart, and the re- 
productive organs. 

Having thus glanced in a cursory manner at the 
form and structure of the Fly, we shall in our next 
enter into a more particular account of its various 
organs. 

c 5 


34 


HUMBLE CREATURES. 


LETTER V. 

THE ANTBNN.® OR FEELERS OF THE FLY ; THEIR STRUCTURE, 
AND VARIOUS THEORIES REGARDING THEIR FUNCTIONS. — 
THE EYES, COMPOUND AND SIMPLE ; THEIR STRUCTURE AND 
USES. 

There is perhaps not a more interesting object in the 
animal creation than the head of a common House- 
fly. If you take a lens, and examine it carefully, you 
wiU find in front of the forehead a pair of short 
antennae or feelers (PI. IV. fig. 1, a, a), organs which, 
in some of the insect races, impart those w'onderful 
instinctive properties that have in this respect raised 
their possessors to a level with the so-caUed higher 
animals, and have rendered them a complete mystery 
to the naturalist. 

The antennae of a fly are well worthy of a particular 
description ; they are composed apparently of three, 
but really of six joints, the third of which (PI. VI. fig. 2) 
is dilated and much larger than the rest ; whilst the 
sixth is furnished with an arborescent tuft of bristles, 
and is termed a plumose joint. 

Wlien the fly is at rest, the first three joints lie in 
a depression of the inseePs head (PI. IV. fig. 1, a, a), 
whilst the plumose joint is seen to protrude: the 


Plate iV 




?v 


I- 







\s'Ti del 


GEBord bth 




John VrxjTst , L . j. ai jt». . 




THE FLY. 


35 


object of this is probably, that the third joint, which 
we shall find to be the most important and delicately 
organized, should thus be protected from dust and 
other causes of injury. The principal feature of interest 
in the anteimae is, that the third joint, when mag- 
nified, is found to be perforated all over with minute 
pvmctures ; these are in reality (as a high magnifying 
power reveals, after the anteima has been bleached 
with chlorine) a series of microscopic sacculi (little 
sacs) extending inwards, and closed in from the air 
by a very thin membrane, and between these sacculi 
there are interspersed on the surface a great number 
of fine short hairs (PI. VI. fig. 2, c). Near the base of 
the joint ai’e three or four larger apertures leading into 
chambered ca\ities, protected at the bottom by micro- 
scopic hairs, and to each of these canties a nerve has 
been traced from the brain, showing that they perform 
some sensory function. 

What, then, you will ask, can be the nature of 
organs so intricate in their construction as these 
antennae ? That is a question which naturalists have 
in vain essayed to answer, and the true function of the 
feelers is a problem still to be solved. Some zoolo- 
gists attribute to them the sense of hearing, others 
of smell, and others again have supcradded to the 
latter sense that of touch. 

These conclusions have been arrived at by com- 
paring the structure of the antennae in various tribes 
of insects with their respective habits of life. They 
have been considered organs of sound chiefly on ac- 


36 


HUMBLE CREATURES. 


count of their anatomical structure ; but Mr. Newport, 
a very careful observer, has also addueed, as an in- 
stanee where the feelers exhibit a sensibility to sound, 
the fact of a beetle, whieh retracts its antennae on a 
sudden noise, and falling down eounterfeits death. 
On the other hand, we have various circumstanees in 
evidence of their taetile and olfactory functions ; 
amongst these may be quoted the Ichneumon-fly 
(one of the Class Hymenoptera, to which the Bee 
belongs), which lays its eggs by means of a sharp 
ovipositor in the larvae of various insects ; on the 
bodies of these, the larv^ae of the Iclmeumon subsist as 
soon as they are hatched. If we observe this insect 
seeking for larvae or caterpillars that inhabit wood, 
old posts, &c., we shall notice that it pushes its an- 
tennae before it into every irregularity of surface until 
it has met with a caterpillar, which it then pierces 
with its ovipositor, and injects one or more eggs. 
Other insects employ the antennae for the same pur- 
pose ; and it has been proved beyond a doubt that the 
sense of smell guides them in depositing their eggs ; 
for some insects, w^hose larvae derive their nourish- 
ment from decaying meat, have been known to com- 
mit the singular mistake of placing them upon plants 
that possess a similar odour, but were totally unsuit- 
able as food for the larvae, in consequence of which they 
died of hunger almost as soon as they were hatched. 
The Bee, again, employs its antennae, or organs of 
smell, in searching for honey : the Ants use these 
organs to point out to each other the locality in which 


THE FLY. 


37 


they have discovered food ; and to suppose that they 
do this by means of signs caused by sound, would be 
attributing to them a power of imparting information 
that could hardly be regarded as the result of instinct. 
The discovery by one of the authors* of this little 
treatise, of the existence of sacs behind the delicate 
membrane covering the pores, and also of the larger 
apertures already alluded to at the base of the third 
joint, may probably throw fresh light upon the 
nature of the antennae. Meanwhile, however, we 
must continue to regard the question of their function 
as still unsettled, and content ourselves with obser- 
ving that they possess some sensory function besides 
that of touch ; either smell, hearing, or both f- 

If the antennae of the Fly haA^e proved a mystery to 
naturalists, equally so have its wonderful eyes been 
the subjects of speculative inquiry. These are five in 
number, tAVO being compound, and of comparatively 
enormous proportions ; for they monopolize the greater 
part of the head, from each side of Avhich they pro- 
trude in a semi-globular form (PL IV. fig. \,bb). 

* Dr. J. B. Hicks : see Transactions of the Linnean Society, 
vol. xxii. p. 147, in which he describes the bleaching process, 
and siniilar organs to those named, in other insects. 

t The sense of hearing has been assigned to them by Bur- 
meister, Cai’us, Strauss-Diirkheim, Oken, Kobineau, Desvoidy, 
and NeAvport j that of smell, or smell and touch, by E^aumur, 
liyonnais, and several French anatomists, Kiister, Eadchson, and 
Vogt. 

It appears to us, that if insects, whose sensibility to external 
influence is knoAAUi to be acute, were confined and tcatched, 
fresh light would be thrown upon the uatm’e of their autennm. 


38 


HUMBLE CREATURES. 


The remaining three are small, simple in their struc- 
ture, and disposed in a triangle on the top of the 
head, between the two compound eyes. We shall 
direct your attention chiefly to the last-named, the 
compound organs. At the first glance, these re- 
semble two small hemispheres, covered with a bright 
brown varnish ; when you examine them more closely 
with a lens, the convex surface appears to be marked 
with a species of network (PI. IV. fig. 1), and, when 
placed under the microscope, this network is found to 
consist of a vast number of convex lenses, disposed in 
regular rows upon the projecting surface. These 
lenses, each of which forms the external surface ot a 
simple, but perfect organ of vision, have been carefully 
counted, and their number amounts to 4000; in 
other insects they are far more numerous. 

If we make a vertical section of one of these com- 
pound eyes, dividing it by an incision across the 
middle of its circumference, and examine it under the 
microscope (PI. IV. figs. 2, 3, 4), we shall find it to be 
constructed as follows : — Each simple lens or facet is 
double convex and hexagonal in form; and behind 
this is a six-sided, transparent pyramid, so attached 
to the facet, that the latter forms, as it were, the base 
of the pyramid directed outwards*. Each p}Tamid 
is imbedded in a dark pigment; so that the light 
which enters one facet may not be dispersed, nor 

* Ryiner Jones calls the pyramid “ an hexaedral prism, 
whose office may be compared to that of the vitreous humour 
of the human eye.” 


THE ELY. 


39 


penetrate into the neighbouring one, and thus cause 
a confusion of rays ; from each facet, or rather from 
the apex of eaeh pyramid, a distinct nerve passes into 
the substance of the eye, and all these nerves meeting 
in one common centre, form a large nerv’ous trmik, 
which conveys the image of sui’rounding objects to 
the brain. You will therefore see that a perfect image 
of external objects is admitted into each facet, which, 
together with its pyramid, partake of the character of 
a telescopic tube ; and that these images most probably 
centre in one point, from whieh the various nervous 
fibres depart. 

Until recently it was a question much discussed 
amongst naturalists, whether these remarkable eyes 
convey to the brain of the Fly, one or many images of 
the surrounding objects; and the existence of the 
three simple eyes already referred to, as being placed 
on the back of the head, by no means tended to the 
solution of this problem. 

Many were of opinion that each facet of the com- 
pound eyes, as also of the simple ones (the former are 
termed stemmata, the latter oculi), conveyed a distinct 
image of external objects to the brain, just for instance 
as we see a series of images on looking through a toy 
mxdtiplying-glass, which is a prism of many facets. 
It has, however, of late been shown that sueh is not 
necessarily the case; for, although it can be clearly 
demonstrated that eaeh facet reeeives a distinct image 
of surrounding objects, yet, from the position of these 
facets, which do not all embrace the same view of the 


40 


HUMBLE CREATURES. 


external field, there can be little doubt that the 
various images meet at a common centre, and are 
conveyed to the brain as a single picture of the sur- 
rounding field. We have only to consider the opera- 
tion of our own eyes, to find a perfect illustration of 
this principle ; for, although we look at one object 
with both eyes, and consequently a distinct image is 
reflected upon the retina of each, we do not see two 
objects, hut only one distinct image is apparent to 
oiir sense. A stiU more remarkable example of the 
fusion of images is, however, foimd in the action of 
the stereoscope, where we actually have two objects, 
or pictures, the images of which first pass through 
two distinct lenses, and into our two eyes, and stiU 
only one clear and prominent figure is carried to the 
brain. 

You will perhaps inquire why such pains have 
been taken to provide the Fly and other insects with 
so many hundreds of eyes, whilst we and the higher 
animals are furnished only with two of these organs. 
Many explanatory replies have been given to this 
question, few, however, being at all satisfactory ; and 
experiments have of late been tried in connexion 
with the function of the simple and compound eyes 
(the former of which are composed of similar parts to 
the single facets of the latter), whereby we should be 
led to the belief that the two sets of eyes do not 
operate alike ; namely, that the one set reflects distant 
objects, whilst the other enables the creature to 
examine those in its immediate vicinity. Further 


THE FLY. 


41 


experiments •will, however, be ueeessary before we ean 
regard this as an established faet*. 

Probably the existenee of the eom pound eyes may 
be attributed to the cireumstauce that insects seek 
their food in the deep tubes, or dim hoUows of flowers, 
and have frequent occasion to enter crevices into 
which the light but partially penetrates. A single 
image reflected in such localities w^ould be faint and 
imperfect; M^hereas a series, collected, as Ave know 
those of insects to be, in one common centre, and 
thence conducted to the brain, would form one clear 
and distinct picture. If, on the other hand, the same 
mechanism Avere employed in the minute eyes of 
insects, as concentrates the external rays in our OAvn 
organs of vision, Ave mean the contractile iris, the 
disposable surface would be almost entirely absorbed, 
and little room left for the admission of rays ; whilst 
it appeal's much more natural and in accordance Avith 
the general structure of insects (Avhich aflbrds nume- 
rous examples of a repetition of similar parts), that 
they should possess a number of simple lenses, than 
that the visual organs shoxdd be furnished Avith the 
mechanical contrivances attached to those of the 
higher animals. If this be so, we may say Avith 
Lyonnet, the great French naturalist, that if it pleases 

* The means employed in this experiment were to besmear, 
with an opaque substance, first one set of eyes in one insect, 
and watch its movements; and then to exclude the light in a 
similar manner from the other set of eyes in another insect, 
and observe the result. The comparison of the moA’ements in 
the two cases led to the above conclusion. 


42 


HUMBLE CREATURES. 


the Creator to eonstruct for the Bee or the Fly 
10,000 eyes, in order the more effeetually to meet the 
creature^s wants, it is as easy for Him to do so as to 
construet a single lens* 


• The Fly is furnished with . . . 
The Mordella (a kind of beetle) . 

The Dragon-fly 

The Butterfly 

The Sphinx Moth 

The Ant 


4,000 facets. 
26,000 facets. 
12,644 facets. 
17,366 facets. 
1,300 facets. 

60 facets. 
(^Burmeister.) 


I 


I 




Ftokosus 
Ifc-ase Ply 




.. X 


u':V^^z J'f-rrvi z^- 


rsf>r 


THE FLY. 


43 


LETTEE VI. 

THE MOUTH OF INSECTS. — THE PHOBOSCIS OF THE FLY. — THE 
MEMBERS OF LOCOMOTION. — WINGS ; THEIR STRUCTURE. — 
WONDERFUL RAPIDITY OF FLIGHT. — HALTERES OB POISERS ; 
THEIR ANATOMY AND SUPPOSED FLTfCTION. — THE LEGS. — 
REMARKABLE ORGANIZATION OF THE FLY’S FOOT. — REPE- 
TITION OF SIMILAR PARTS IN THE ORGANS DESCRIBED. 

Before passing from tlie consideration of the Fly^s 
head, we have still to examine another organ, namely 
that of nutrition, which is termed the probostis ; this 
is situated in front, towards the under surfaee of the 
head, and when not in use, lies folded up in a de- 
pression, out of the way of injury. 

In order more clearly to explain the character of 
this organ, we must briefly describe the typical struc- 
ture of the mouth of insects generally. Those that 
masticate their food are usually furnished with the 
following parts; — 1. an upper lip {labrum), and a 
lower lip {labium), which work together in a similar 
manner to our own, and when closed conceal the 
remaining parts. Between these lips there is, 2. a 
pair of jaws {mandibulcB), and, 3. a smaller pair {max- 
illa), which operate laterally and masticate the food ; 
and, 4. we find two pairs of feelers j the first {maxil- 


44 


HUMBLE CREATURES. 


lary palpi) attached to the maxillae, and the second 
{palpi labiales) connected Avith the lower lip. These 
feelers enable the insect to test the nature of its food. 
Now, when an insect does not reduce its food by 
mastication, but, as in the case of the Fly and others, 
obtains it by suction, all the organs just enumerated 
appear to be Avauting, and a proboscis or suction- 
pump is substituted, as being better adapted to the 
changed character of the food on w'hich the insect 
subsists. On examining it more closely, howcA^er, we 
find that the proboscis is, after all, but a transforma- 
tion of the maxillary organs just refeiTed to as exist- 
ing in the generality of insects. Let us take that of 
the House-fly for example. The proboscis of the Fly 
(PI. IV. fig. 1, c, and PI. V. fig. 1) consists of a tubu- 
lar bag, formed of thin transparent membrane, Avhich 
arises firom the front of the head, and is dilated at its 
extremity, forming at this part a large sucking disc. 
This bag is the converted portion of the loAver lip 
{labium), known as the ‘ ligula,’ or tongue, a term 
that is often applied to the proboscis itself, and is 
furnished inside with a very complicated apparatus, 
to enable it to perform its functions. The terminal 
sucking disc (PI. V. fig. 1, a) is so constructed as to 
gather the fluids and attract them towards an aper- 
ture at b, Avhich leads to the throat or gullet (to be 
described hereafter) ; and in a groove on the under- 
side of this tubular portion are two sharp bristles or 
lancets, c, and beneath these, one more lancet, less 
pointed, but still sharp {b). The apex of the latter is 


THE FLY. 


45 


pierced by an opening, as above mentioned, that 
passes up its centre and conducts to the gullet, which 
runs through the base of the tubular bag. These 
lancets are the representatives of the 'maxillae’ and 
'mandibles,’ and are employed to puncture the ob- 
jects from which the Fly sucks the juices. On the 
under surface of the disc are a number of lines run- 
ning fi’om the cfrcumference to the centre, as in 
PI. V. fig. \,dd‘, and when these are highly magnified, 
they are found to be a number of ribs, forming about 
three-fourths of a tube, the open portion of which 
faces downwards, so as to admit the liquid food ; 
when the fluid has entered it passes along, probably 
by capillary attraction, to the centre, close around 
which all the tubes open. Here it enters the aper- 
ture in the single lancet, finally to reach the gullet. 
These ribbed tubes are connected together by very 
delicate lines, springing from the points of the ribs, 
as represented in PI. V. fig. 2. Besides the piercers, 
the proboscis is furnished with a pair of well-defined 
maxillary palpi (PL V. fig. 1, e), which enable it to 
test the character of its nutriment; and the entire 
apparatus is covered with a great number of fine hairs, 
and permeated by respiratory tubes [trachea:), the 
nature of which we shall consider hereafter. 

You may, perhaps, not have been aware that the 
harmless little Fly possesses such weapons as the 
aforesaid lancets ; but if you have ever been stung by 
one about the time when they are dying out, and have 
seen the drop of blood arising from the wound, you 


46 


HUMBLE CREATURES. 


would feel satisfied that such an effect can only be 
produced by a sharp instrument. The eye, antennae, 
and proboscis of the Fly are all objects of great in- 
terest to the microscopist, and may be found, pre- 
pared in slides, in the cabinet of almost every col- 
lector. They are obtainable at a trifling cost* ; a 
low power, and consequently an inexpensive instru- 
ment f, suffices to show their structure ; and if 
you desire to become acquainted with the physiologj^ 
of the insect, or even to employ a leisure hour 
agreeably, you will find them well worthy of a careful 
inspection. 

Having made ourselves tolerably well acquainted 
with the various organs of sense and nutrition situated 
upon the head of the House-fly, let us now take a 
cursory glance at the members of locomotion, all of 
which we shall find appended to the second dmsion 
of the body, the thorax or chest. In our fourth 
letter we enumerated the three parts into which this 
section of the Fly^s body is divided, and mentioned 
that the little creature possesses three pairs of legs, 
oiie pair of wings, and a pair of organs termed halteres 
or poisers ; the first pair of legs being situated upon 
the prothorax, or anterior ring ; the second pair and 
the wings upon the mesothorax, or central ring ; and 

* One shilling and sixpence each. The objects which have 
sensed to illustrate this treatise were prepared by Mr. Purkiss 
of Tottenham. 

t A microscope may be purchased for lOs. 6d. of sufficiently 
high power for this purpose. 


THE FLY. 


47 


the last pair of legs and halteres upon the metathorax^ 
or last subdivision of the ehest. 

The most important of these members, looking at 
the habitat of the Fly, are undoubtedly the wrings. 
They consist, as you are well aware, of a pair of mem- 
branous expansions; each wing is composed of an 
upper and lower transparent membrane, and between 
these two layem the blood-vessels and respiratory 
tubes {tracheat) ramify, so as to form a beautiful net- 
work for the support of the extended membranes. 

You will perhaps be somewhat surprised to hear 
that the wings of our little Fly, to whose structure you 
may never have devoted a single moment’s thought 
during your lifetime, have been so carefully investi- 
gated, and received so much of the anatomist’s atten- 
tion, that not only has each branch or ‘ nervule,’ as 
these ramifications (PL VI. fig. 1, a) are termed, but also 
each intervenmg portion of the transparent membrane 
has been deemed worthy of receiving a distinct de- 
signation. To enumerate these would be to trespass 
beyond the limits and intention of this little treatise ; 
but we mention the fact, in order to show how much 
there is to be learnt in creatures of even the most 
humble character. 

We may here also observe, that near the root of the 
wings, where these are joined to the body, there have 
been discovered a great number of small vesicles, the 
nature of which is still a mystery ; but as we shall 
have occasion to describe them more fuUy when 
treating of the halteres, where they are also found. 


48 


HUMBLE CREATURES. 


we shall here simply allude to their presence in the 
members now under consideration. But although we 
pass thus rapidly over the anatomy of the wings, as 
being of too scientific a character for tliis treatise, we 
must not omit to refer to the remarkable effects that 
they produce, and vnU dwell for a moment upon their 
Avonderfid operation. 

The rapidity of their vibrations is something in- 
credible, and the number of these within a given 
space of time has been approximately ascertained by 
the following experiment. When a spring is caused 
to vibrate a certain number of times, it emits a par- 
ticular tone, and, as the number of its vibrations is 
increased or diminished, this note rises or falls in 
pitch. Now, this vibration being analogous to that of 
the wing of an insect, which al^o emits a musical sound, 
an apparatus has been constructed wherein a multi- 
plying- wheel, with a given number of cogs, against 
which a spring strikes, is made to revolve rapidly. 
A note being thus produced, varying in pitch accord- 
ing to the rapidity of the revolutions, the velocity is 
accelerated or retarded until this note is the same as 
that proceeding from the wings of the insect, and by 
an easy calculating process the number of vibrations 
may be thus ascertained. 

Messrs. Kirby and Spence inform us that “an 
anonymous writer in Nicholson’s Journal calculates 
that in its ordinary flight the common House-fly 
( M. domestica) makes with its wings about 600 strokes, 
which carrj'^ it 5 feet, every second ; but if alarmed, 


THE FLY. 


49 


he states, “their veloeity ean be inereased six- or 
seven-fold, or to 30 or 35 feet per seeond. In this spaee 
of time a raee-horse would clear only 90 feet, which is 
at the rate of more than a mile per minute. Our little 
riy, in her sAviftest flight, will in the same space of 
time go more than the third of a mile. Now, compare 
the iiifinite difference of the size of the two animals 
(ten millions of the Fly would hardly counterpoise one 
racer), and how wonderful will the velocity of the 
minute creature appear ! Did the Fly equal the race- 
horse in size, and retain its present powers in the ratio 
of its magnitude, it would traverse the globe with the 
rapidity of lightning ! ” 

Every observer must have remarked with what ease 
the fly plays around the head of a horse in rapid 
motion; and Vogt says the Gad-fly flies with a speed 
equal to that of a railway-tram. Though this may ap- 
pear exaggerated, the calculation will not seem so far 
from the truth, when Ave notice that, Avhilst the moving 
body proceeds in straight lines, the insect performs 
numerous gyrations at the same time, thereby con- 
siderably increasing the distance. Some allowance 
must be made for the assistance the insect derives 
from the stratum of air put in motion by the pro- 
gression of the object, as also by the momentum 
gained by occasionally touching the object with which 
it is travelling. The common Gnat {Culex pipiens) 
has a much higher rate of vibrations, Avhich are com- 
puted at many thousands per second. 

In such insects as possess tAvo pairs of wings, e. g. 


0 


50 


HUMBLE CREATURES. 


the Butterfly, Beetle, Dragon-fly, &c., the second pair 
is situated upon the metathorax, the third ring; but 
in the Fly, which is only furnished with one pair, the 
place of the second is supplied by two little members 
termed haltcres, or poisers. These appear to be rudi- 
mentar}’ wings, ai’e protected by a pair of horny scales, 
and, seen with the naked eye, they resemble two 
globules, which are kept in a state of constant vibration 
whilst the insect is on the wing. On being detached, 
however, and examined under the microscope, they pre- 
sent a clubshaped appearance (PI. VI. fig. 3), and their 
base is found to be studded all over with microscopic 
vesicles disposed in regular rows upon the surface. 
Between these vesicles, as in the case of the antennse, 
numerous hairs are interspersed Muth great regvdarity. 
It has been found that two large nerves proceed from 
one of the principal nervous centres in the insect (the 
thoracic ganglion) into the halteres ; and from these, 
minute branches have been traced to all the vesicles 
upon the surface : from this it must be inferred that 
these vesicles (as well as those in the wings, with 
which nerve-fibres also communicate) are organs of 
sense, and it is believed by the observers who dis- 
covered them* that they are the organs of smell. 
Should this prove to be the case, there will be less 
difficulty in determining the true character of the 
antennje, in which the vesicles are depressed, as stated 

* Mr. Purkiss and Dr. J. B. Hicks : see papers by latter in the 
.Toumal of the Linnean Society, vol. i. No. 3; and Linnean 
Society Transactions, vol. x.xii. p. 144. 





plateTT 





ei< Sc 



fieri' Wer^t 


THE FLY. 


51 


in a former letter ; whilst those in the halteres and 
wings project from the surface (PI. VI. fig. 3^ a and h), 
nerves having been traced to both sets of organs. 

The last, but by no means the least interesting of 
the Fly’s members, to which we shall draw your atten- 
tion, is its leg, and more especially the final or 
“ tarsal ” joint. The leg of the Fly (and indeed of 
insects in general) is divided into five distinct limbs 
or joints : the first of these is the “ coxa,” or hip, by 
which the leg articulates upon the body (PI. VI. 
fig. 4, a) ; then the trochanter,” a short round 
joint (PI. VI. fig. 4, d) ; next the femur,” or thigh, 
the largest of the five joints (4, c ) ; the tibia,” a 
somewhat thiimer member (4, d) ; and lastly, the 
“tarsus,” or foot (4,/). None of these are distin- 
guished by any feature of peculiar interest, excepting 
the last-named ; but that one we shall find quite de- 
sendng of a closer examination. 

The “tarsus” or foot of the Fly is subdivided into 
five joints, the final one being furnished with that 
remarkable apparatus which enables the insect to 
walk upon what appear to us perfectly smooth or 
pobshed surfaces, and also to progress in a position 
opposed to the laws of gravity. 

This apparatus consists of two moveable claws 
(PI. VII. fig. 1), resembling a co-NY’s horns in shape, 
which the insect can affix to any little eminences or 
depressions that present themselves in its course ; and 
further, of a pair of membranous expansions, termed 
“ pulvilli,” or, familiarly, pads, which, when magnified 

D 2 


HUMBLE CREATURES. 


f,9 

(same figure), resemble the broad termination of a 
child’s battledore formed of parchment. Until re- 
cently, these p^llvilli, which are furnished with innu- 
merable hairs, were supposed to operate as suckers ; 
but the higher powers of the microscope have revealed, 
at the termination of each of the numerous hairs that 
cover the surface, a minute expansion, which is kept 
moist by a fluid exuding from the extremity* ; and 
the belief now prevails that, whilst each single hairlet 
(PI. VII. fig. 1, a) serves as a sucking disc, the two 
])idAulli themselves act as cushions for the preserva- 
tion of the larger hooks (which would otherwise 
become abraded), in a similar manner to the soft 
cushions that protect the sole of a cat’s foot, and 
enable it to tread so lightly. 

This view is strengthened by the examination of 
the foot of Dytiscus marginalis, one of the large 
Water-beetles, in which these small suckers are deve- 
loped in a remarkable degree ; and also to some extent 
by the ambidacral suckers that serve as members of 
locomotion in the Star-fishes and other Echinoderms, 
and the terminal cushions upon the toes of the Chmb- 
ing-fi’og {Hyla arborea), in all of which a power is 
imparted similar to that possessed by the House-fly. 

With this description of the Ely’s foot, we shall 
conclude our cursory review of its external parts; 
and, before quitting this portion of the subject, let us 

* For this discovery we are indebted to Mr. Hepworth : see 
his paper in the Quarterly Journal of Microscopical Science, 
1854, vol. ii. p. 158. 


THE FLY. 


53 


again draw your attention for an instant to a remark- 
able peculiarity in its most important organs, one to 
which we have already made passing allusions, namely, 
to the repetition of similar component parts in the 
structure of these organs. The eyes with their 
facets, the antennae, wings, and halteres with their 
numerous vesicles, and lastly, the pulvilli Avith the 
appended suckers, all present examples of that pecu- 
liarity of structure which has proved such a difficult 
problem to naturalists ; and although bundles of 
nerves have been traced to the three sensory organs, 
yet neither the searching powers of the microscope 
nor a comparison of their structure in the various 
races of insects, have enabled anatomists fully to 
understand and estimate their true properties. A 
closer examination of their habits, however, com- 
bined with what is already ascertained in regard to 
their anatomy, wdl doubtless soon clear up the 
mystery; and should you be inclined to enter the 
ranks of observers, you Avill find the field to be one of 
unbounded study and interest. 


54 


HUMBLE CREATURES. 


LETTER YII. 

THE ANATOSry OF THE FLY. — ITS ORGANS OF DIGESTION ; OF 
CIRCULATION ; OF RESPIRATION. — WONDERFUL STRUCTURE 
OF THE SPIRACLES OR BREATHING-HOLES, AND TRACHE.E 
OR RESPIRATORY TUBES. — NERVOUS SYSTEM. — CONSIDERA- 
TIONS UPON THE NERVOUS SYSTEM OF THE HOUSE-FLY 
AS COMPARED WITH THAT OP ITS LARVA AND OP THE 
WORM. 

From the foregoing description of the external mem- 
bers of the House-fly, you will have perceived how 
well adapted they are to its aerial existence ; and if 
we now investigate its internal structure, we shall see 
that the vital organs arc so disposed and constructed 
as also to facilitate its movements in the atmosphere. 
Les us take each function seriatim. First, as regards 
that of nutrition. We have fully considered the pro- 
boscis, by which the food is procured; thence it passes 
into the throat, which is muscular, and forms the 
entrance into a species of crop (PI. III.) situated at 
the left side of this throat, and opening into it is a 
lock-necked food-reservoir, not inaptly termed the 
paunch, and which is adapted, by its conformation, to 
facilitate the ruminating process*. 

• L^on Dufour, Anatomie G(|n6rale des DiptSres, .“Vnii. des 
Sci. Nat. i. p. 244; Vogt, Zoologische Briefe, vol. i. p. 698. 


Plate VI! 



J SaiztueUon dal 


John Vaji Vo or St , L on ^ on 


CH Ford IztiL 


i 




THE FLY. 


55 


From this crop the food passes into an extended 
stomach, and thence into a long convoluted hoAvel, to 
which are attached numerous biliary tubes, and which 
terminates in an expansion called the cloaca. This 
complicated digestive apparatus extends throughout 
the whole body, the throat eommencing in the head, 
and terminating in the thorax, in which is also situ- 
ated the stomach and its appendages; whilst the 
long winding intestine is found, along with the other 
viscera, in the last or abdominal section of the body. 
Instead, therefore, of a simple alimentary canal, pass- 
ing in a straight line from end to end of the body, as 
we found in the Worm, the lowest of the ai*ticulate 
series, we have here four distinct dmsions in the di- 
gestive apparatus, — a progressive step in the develop- 
ment, with which we shall find the other vital organs 
in pei’fect accordance. In regard to the circulation of 
the blood, for instance, you wiU reeollect that the 
Worm possessed one undivided contractile tube, which 
extended along the back, and, jjerforming the func- 
tions of the heart, propelled the vital fluid along the 
whole body, after which it was again collected in 
another canal running along the ventral portion of 
the animal. Now in the Fly, although the principle 
of operation is precisely the same, the organs that per- 
form the function are far more highly developed. The 
dorsal vessel (heart) extends along the whole body, 
just within its external covering, and differs from 
that of the Worm inasmuch as that portion of it 
which is situated in the third or abdominal section of 


56 


HUMBLE CREATURES. 


the body, is not only contractile, but at the same time 
divided into a series of chambers (PL III.) opening 
into one another by means of valves ; the portion of 
the dorsal vessel, however, which passes through the 
thorax, is a simple contractile tube resembling that 
found in the Worm. The blood is forced, by the con- 
tractility of the dorsal vessel, from the tail towards 
the head, first passing from chamber to chamber in 
the abdominal segment ; for the valves which connect 
these are so constructed as to admit of its flowing 
forward, but not allowing it to return. From the 
abdominal chambers it enters that portion of the 
dorsal vessel situated in the thorax, and is thence pro- 
jected forward into the head. A ventral tube is also 
present, which, as in the Worm, conveys the blood 
from the head backwards in the direction opposed 
to that which it pursues in the dorsal heart; but, 
in consequence of the opaque covering of the Fly 
(and other insects), anatomists have not been able 
fully to trace the circulation. A surprising circum- 
stance is, however, kno^vn with regard to this func- 
tion ; and that is, that in some portions of the body 
the blood circulates in cavities, unconfined by any 
vessels whatever, and bathes the different viscera. It 
then collects in the vicinity of the dorsal vessel, the 
chambers of which are furnished with valves at each 
side (as well as those which connect one chamber 
with another) ; and this second set of valves is also 
so constructed that they admit the blood from -with- 
out, but prevent its egress. It is also ascertained 


THE FLY. 


that the central trunk gives out numerous branches, 
which convey the blood to the different members of 
the body. 

Intimately connected with the circulating system 
is that of respiration] and when you consider that 
the Fly is formed to be a denizen of the atmosphere, 
and that its specific gravity is necessarily one of the 
most important features in connexion with its exist- 
ence, you -nill not be surprised to hear that the appa- 
ratus by which the air is admitted and allowed to 
circulate through the body, is very beautiful, and 
displays marked evidences of a designing hand. If 
you examine the under surface of the Fly with a 
pocket-lens, you Avill find extending along the middle 
of the abdomen a membranous band that divides the 
horny rings of which the covering is composed into 
two parts, and at each side of this membranous divi- 
sion (but on the rings themselves) you will perceive a 
row of minute punctures which penetrate the so-called 
chitine integument of the body. These little aper- 
tures, a pair of which is situated upon each abdominal 
ring, and two pairs upon the thorax, in contiguity with 
the members, have been variously denominated 
spiracles, stigmata, or breathing-holes, and through 
them the air is admitted into the body ; the respira- 
tory operation is effected in a somewhat similar 
manner to the same process in the higher animals, 
namely by muscular dilatation and contraction, in 
this case of the abdominal region. 

Through the spiracles, which we shall find to be 

D 5 


58 


HUMBLE CREATURES. 


beautifully constructed organs, the air passes into 
tine tubes called tracheee, whence it is conducted into 
other receptacles varying in form and size. Two of 
these are capacious sacs, occupying a considerable 
portion of the abdomen (PL III.) ; whilst one main 
tracheal or tubular vessel extends along each side of 
the abdomen and thorax; and from these, minute 
branches ramify in such a manner as to convey the 
needful supply of air to every part of the insecPs 
body. Let us first examine the spiracles or stigmata, 
that admit the air into the body. If these had been 
simple incisions or apertures in the outer integument, 
they would have admitted along with the atmosphere 
minute particles of dust, and the tracheal tubes would 
soon become so choked up as to prevent the free 
circulation of the air. To obviate this difficulty, 
therefore, nature has protected the entrance by a 
species of sieve or screen, which is as beautiful as it 
is effective, and is formed in the following manner : — 
From every part of the circumference of the apei-ture 
there proceed towards the centre a great number of 
short arborescent trunks (PI. VII. fig. 2), whose innu- 
merable minute ramifications become so interlaced 
as to form a complete network across the entrance, 
and beyond which every particle of foreign matter is 
effectually prevented from passing. But when the 
air has entered the tracheae or circulating tubes, 
another difficulty presents itself ; for these tubes are 
necessarily very compressible, and the rapid move- 
ments of the insect must often cause them to collapse 


THE FLY. 


59 


in various parts, where of course tlie circulation of 
the air is tlien aiTCsted ; and unless some means were 
employed to re-open the tube, its lining membrane 
would be very liable to adhere, and cause it to re- 
main permanently closed. Nothing can be more de- 
licate and simple than the contrivance by which this 
obstacle is overcome, — a contrivance, that we find 
constantly imitated in our every-day life. When one 
of the larger tracheje is magnified about 400 diameters, 
it is found to consist of a double integument, between 
which a close continuous coil of hairlike fibre is situ- 
ated, which supports the tubes in a similar manner 
to the coil of wire in gas- or speaking-tubes. This 
coil (PI. VI. fig. 6) adds considerably to the elasticity 
of the air-vessels ; and when these collapse tlu’ough 
the movements of the insect, it prevents the opposed 
sides from adhering permanently, and causes them to 
resume their tubular form as soon as the pressm’e is 
removed. 

In the distribution of the tracheae we find the same 
wise arrangement that characterizes every other por- 
tion of the internal economy of the Fly. The abdo- 
men, being the heaviest section of the body, on ac- 
count of the mass of viscera that it contains, has its 
specific gravity considerably diminished by being fur- 
nished with two large air-bladders (PI. III.), as v'ell 
as two tracheal tubes of considerable size, that pass 
along either side of the body ; whilst the thorax, on 
which the wings are situated (and which of them- 
selves add to the buoyancy of the insect), is only pro- 


60 


HUMBLE CREATURES. 


videfl internally with a pair of lateral tubes ; in both 
cases the main tracheee give out innumerable minor 
brancheSj as already noticed, around which the blood 
flows, becoming by that means thoroughly oxy- 
genized. 

But if the nutritive and circulating systems of 
the House-fly afford, through their advanced organi- 
zation, a remarkable contrast with those of the 
Worm, still more striking shall we find the indica- 
tions of a comparatively high degree of development 
presented by the nervous system of the insect. This 
portion of its anatomical structiire (PI. VI. fig. 1, b b) 
consists — 1, of the brain, other^vise termed the 
cephalic or supra-cesophageal ganglion, which is com- 
posed of two small masses of nenous matter situated 
(as the foregoing expressions denote) in the head, 
“ above the oesophagus’’ or throat. From the sides 
of this ganglion there proceed two large nerves to 
the eyes, and in front a nerve to each antenna, and 
some smaller ones to the parts of the proboscis. 
2. From the lower portion of the brain a small 
nervous chord passes downward on each side : these 
surround the gullet and form below it, 3, the sub- 
oesophageal ganglion ; from which again, 4, the two 
nervous chords, united into one, pass to the centre 
of the thorax, where we find, 5, a large mass of 
grey matter, called (from its position) the thoracic 
ganglion. 

From this large nervous centre nen'es are given ofi' 
in pairs (see PI. VI. fig. 1, 6 A) in all directions, nz. 


THE FLY. 


61 


a pair to tlie anterior legs, another to the wings, a 
third pair to the seeond legs, a large pair (the largest 
of all) to the halteres, and two nerves to the posterior 
legs. Besides these, the thoracic ganglion also gives 
out a bundle of nerves (an’anged bilaterally) into the 
abdomen ; a single one, however, passing through the 
centre of that section of the body, at the termination 
of which it is forked, and the two extremities pro- 
ceed to the reproductive organs on each side. Thus 
you will perceive that every portion of the Fly’s body, 
every organ and member, is provided with its special 
nerve ; and if we now compare this portion of its phy- 
siology with the nervous system of the Worm (Let- 
ter III.), and of the Fly itself in its lannl stage, we 
shall find the comparison of their structure to be 
interesting and instructive. The brain of the Worm 
resembles that of the Fly, and also gives off two 
chords, which unite and pass along the ventral sur- 
face of the body. In each ring we foimd bilateral 
branches proceeding from the central chord ; and 
these branches being often repeated, and of a uni- 
form size, aflford evidence, upon the principle already 
referred to*, of the humble organization of the 
Worm. 

If we next take the larva, or grub of the House- 
fly, the body of Avhich also consists of soft rings, as 
in the Worm, we shall find in each ring, and situated 

• In treating of the eye of the Fly, we explained that a repe- 
tition of similar parts was an evidence of its low organization, 
as compared with the higher animals. 


62 


HUMBLE CREATURES. 


upon tlie central chord, a nervous ganglion, from 
which bilateral branehes proeeed in a similar manner 
to those in the Worm, showing a somewhat superior, 
but still low" stage of development. But now", if we 
compare these struetures with the nervous system of 
the Fly, we shall find a marked progress, indicated 
by a concentration of the chief nervous centres, and 
by a great disproportion in the size of the various 
bilateral branches. The only two important centres 
are the cephalic ganglion (brain) and that in the 
thorax, the latter being produced by a fusion of all 
the larval ganglia, except the brain and suboesophageal 
ganglion. The nerves, too, differ considerably in their 
proportions, owing to the tmequal development of the 
organs and members to which they proceed. The 
optic, which has already been desci’ibed, is enormously 
developed, to supply the numerous facets of the com- 
pound eye. Next in size is that w"hich proceeds to 
the halteres, then that to the wings, w"hereby the 
importance of these organs is sufficiently indicated ; 
and the remaining nerves are of compai’atively small 
dimensions. 

We have thus dwelt upon the nen'ous system of 
the Fly, not only for the purpose of showing its 
analogy with that of the Worm, and the points of 
difference between them, but also because the con- 
sideration of this part of their anatomy, along with 
that of the larva of the Fly, in reality comprises a 
review of the nervous system of the w'hole series of 
Articulated animals, all of which more or less nearly 


THE FLY. 


63 


resemble that of one or other of these three forms ; 
and we shall now conclude our account of the House- 
fly with a description of its wonderful powers of re- 
production and some details of interest connected 
with its hfe-histoiy. 


64 


HUMBLE CREATURES. 


LETTER VIII. 

LIFE-HISTORY OP THE FLY. ORGANS OF REPRODUCTION. — 

MODE OF DEPOSITING ITS EGGS. — TABLE SHOWING ITS RE- 
MARKABLE REPRODDCTITO POWERS. — THE LARVA; THE 
PUPA. — TRANSFORMATIONS. — THE PERFECT FLY ; ITS 
HABITS. — STRANGE FATAL DISEASE TO V'HICH IT IS SUB- 
JECT. — ITS USES AS A SANATORY AGENT, ETC. — TRANS- 
FORMATION OP MATTER IN THE ANIMAL CREATION. — RE- 
FLECTIONS UPON GEOLOGICAL FACTS IN CONNEXION WITH 
THE FLY. — CONCLUSION. 

However cursory the foregoing review of the won- 
derful structure and varied functions of the Fly may 
have been, stdl we think you will experience some 
difficulty in realizing the idea that we have been de- 
scribing that familiar insect whose swarms invade 
our parlours and store-rooms as the summer months 
approach, and become so formidable that we are 
obliged to resort to various expedients in order to rid 
ourselves of their presence. Although this is the 
most unfavourable aspect under which the Fly pre- 
sents itself to our notice, yet the very multitudes that 
force themselves into our dwellings, and cause us so 
much annoyance, suggest to the reflecting observer 
considerations which are far from uninteresting. 


Plate VUl 


Rgl. 



J. Saonuftbaa dd 


W Wr=;.f --irtjj. 


J^'Hu Vau Vl*o!r?Tt, . (.todoit 



THE FLY. 


65 


The questions that you will naturally put to your- 
self when you enter your breakfast-room, and find 
that the little intruders have already taken possession 
of your choicest viands, are : ‘‘ Whence come these 
myriads of insects, of wliich, a few days since, scarcely 
a single one was visible ? and what has been their 
previous career?” We shall endeavour briefly to 
answer these queries, and to detail a few of the best- 
known facts in regard to the life-history of the Fly. 

Few persons are aware,” (to quote the words of 
an old German writer* on the subject) “ that these 
insects, which swarm around their heads, had pre- 
viously crept under their feetj” but that such is the 
case, we have already mentioned in treating of the 
metamorphoses which the Fly undergoes, and of the 
analogies that exist between its larva and the fully- 
developed Worm (Letter IV.) ; and a reference to 
this portion of the subject leads us first to consider 
the mode of reproduction in the Fly, and of the 
extraordinary powers that it possesses to multiply its 
species. 

As we have glanced at the general anatomy of the 
Fly, we may here mention, with reference to its 
organs of reproduction, that they are never united in 
the same creature, as we found to be the case in the 
W orm ; but in this insect the sexes are perfectly 
distinct, the female being recognizable by the pre- 

• Keller, ‘ Geschichte der gemeinen Stubenfliege’ (trans. 
“ History of the Common House-fly.” A copy may be found in 
the British Museum). 


G6 


HUMBLE CREATURES. 


sence of a little tube {ovipositor), situated at the end 
of the abdomen. This organ is formed of three or 
four rings, which the fly can protrude or retract, 
after the manner of a telescope, and employs for the 
purpose of depositing her eggs. Internally the organs 
of the female consist of a pair of branching tubes, in 
which the ova are developed, whilst the male is fur- 
nished with tubes and glands necessary for the deve- 
lopment of the fructifying elements, these organs in 
both sexes being situated in the abdominal section of 
the body. Beyond this there is nothing of interest 
to the general reader in this portion of the Fly's 
anatomy. 

Keller, the naturalist, to whom we have just re- 
ferred, and who studied the history of the Fly with 
considerable attention, tells us that the female deposits 
her eggs six or eight days after impregnation. This 
she usually does in such decaying substances as her 
instinct denotes to be suitable for the nourishment of 
her larvae, as, for example, the heaps of vegetables 
and other substances that are found in the neigh- 
bourhood of our dwellings. 

“ If," says Keller, “ the Fly be enabled to choose 
the place which suits her best for the deposition of 
her eggs (as for instance, in my sugar-basin, in which 
I placed a quantity of decaying wheat), she takes a 
correct survey of every part, and selects that in which 
she believes her ova Avill be the best preserved, and 
her young ones well cared for. If there were too 
much moisture, the maggots would be drowned ; if too 


THE FLY. 


67 


little, the first drought would eause eggs and larvae to 
become desiccated. Having chosen a suitable locality, 
one neither too wet nor too dry, she protrudes her 
little ovipositor, and therewith lays her eggs, by the 
side of, and upon one another, with the same pre- 
cision as the cleverest hands would arrange larger 
objects ; she then sits perfectly still, without moHng 
a single member of her body excepting her ovipositor ; 
indeed it would appear as though she were not quite 
conscious whilst this operation is being performed, 
for so long as she is not absolutely touched, one may 
approach her as nearly as one likes, Avithout causing 
her to exhibit the least symptom of alann. During 
this operation, which lasts half a quarter of an hour 
(a few minutes more or less), she lays 70, 80, or 90 
eggs.” Generally speaking, the greater number of 
insects die as soon as they have deposited their eggs ; 
but Keller’s observations led him to believe that this 
is not the case with the Fly, for he retained several 
alive in a glass for some days after oviposition Avas 
completed, and he, as Avell as other naturalists, be- 
lieve that the insect deposits her eggs three or four 
times during her life, the duration of which is a few 
Aveeks or months. 

Assuming that the Fly deposits 80 ova at a sitting, 
and that she performs this operation four times during 
her life, Keller has draAvn up the following curious 
table, from Avhich it would appear that a single female 
might in one season be the progenitrix of upwards of 
tAvo million flies ; — 


68 


HUMBLE CREATURES. 


“ The parent Fly lays her eggs four times 
during the summer, and each time she 

deposits 80 eggs, making 

Now, it must be assumed that half of these 
are females, so that at each of the four 
depositions 40 females are bom : — 

(1) The first eighth, or the 40 females re- 

sulting from the first deposition, lay 
again four times during the season, 

making together 

Again, the first eighth of these, or 1600 
females, deposit three times, making . 
The second eighth, or 1600 females, de- 
posit twice, malting 

The third and fourth eighths, or 3200, 
deposit once, making 

(2) The second eighth, or 40 females of the 

first deposition, lay three times more, 

making 

One-sixth of these, or 1600 females, de- 
posit again three times, making . . 
The second one-sixth, or 1600 females, 
deposit again twice, making . . . 

The third one-sixth, or 1600 females, 
deposit again once, making .... 

(3) The third eighth of the first laying, or 

40 females, lay twice, making . . . 

Of these, one-fourth, or 1600 females, 
deposit twice, making 

(4) The fourth one-eighth of the first depo- 

sition, say 40 females, deposit once 

more, making 

Whereof one-half, say 1600 females, de- 
posit at least once, making .... 


320 flies. 


12,800 

384.000 

256.000 

256.000 

9,600 

384.000 

256.000 

128.000 
6,400 

256.000 

.3,200 

128.000 


‘Total . . . 2,080,320 flies.” 


* Keller makes the addition 2,208,420, which appears erro- 
neous ; but for our purpose it is immaterial. Another naturalist 


THE FLY. 


69 


Although the foregoing calculation is quite suffi- 
cient to account for the immense swarms of Flies 
that make their appearance during the summer and 
autumn months, yet these would be considerably in- 
creased were it not that, from various causes (such as 
drought, flood, &c., and the rapacity of birds and other 
animals that prey upon them), a considerable number 
of the eggs thus deposited are never hatched; or if 
hatched, the larvaj are, from similar causes, destroyed 
in that stage, and do not attain the imago form. The 
eggs are hatched a few days after they are deposited ; 
and if you wish to obtain a tolerably accurate idea of 
the appearance of the larva that proceeds from them, 
you have but to examine with a pocket-lens one of 
the well-known long white maggots, commonly termed 
“jumpers,” which are found in decaying cheese, and 
afterwards become converted into a small black Fly 
{Piophila) belonging to a kindred group; or one of 
the ordinary maggots found in ham when in a state of 
decay. 

The body of the larva (PI. VIII. fig. 1 & I, a) is 
divided into thirteen rings, of which the anterior, or 
head, is furnished with a pair of hooked jaws, and 
curious globular palpi (PI. VIII. fig. 4), and the 
second bears a pair of rudimentary feet (fig. I a, 2). 

The jaws, along with the remaining apparatus 
situated upon the first ring, are capable of being 
retracted, and they then present the appearance de- 
computes the number of ova deposited to be above 2,000,000,000, 
and Scbwammerdam counted 140 eggs in the body of one Fly. 


70 


HUMBLE CREATURES. 


lineated in fig. 5 ; or Avlien fully extended, as at 
fig. 6. 

On the posterior portion of the last ring (fig. 1 a, 13), 
as well as at the side of every other segment of the 
larva, are to be found spiracles or respiratory holes 
symmetrically disposed in pairs ; and within the body 
may be seen a very perfect system of tracheae or 
respiratory tubes, two or three of which are visible 
in fig. 6, t, and which serve to aerate the circulating 
fluid. 

With the exception of these organs the larva 
presents the appearance of a smooth Worm, void of 
members of any kind ; but when the microscope is 
brought to bear in its examination, it is found to be 
covered with a vast number of diminutive hooks, 
disposed in regular rows or circlets upon each ring 
(PI. VIII. figs. 1 a, 5 & 6), which remind us forcibly 
of the hooks upon the body of the worm, and thus 
render the analogy between the two living objects still 
more remarkable. 

Whilst in this state, the larva is constantly de- 
vouring the substances in which it was hatched, and 
increases rapidly in size \ it is, however, asexual, i. e. 
incapable of reproduction, and in a few days assumes 
the pupa-form. This change is effected by the 
hardening of the outer skin, which becomes bronn 
and tough, inclosing the larva in a little bright 
barrel-shaped case, divided into rings or segments 
(PI. VIII. fig. 2), and it is then to all appearance 

lifeless. 


THE FLY. 


71 


Whilst the insect is in this its second or pupal 
condition, that remarkable metamorphosis is taking 
place in its internal as well as external structure, 
which raises it from the type of a Worm to that of a 
highly-organized insect, a change to which we have 
more than once referred in the course of this treatise. 

The simple jaws of the larva are replaced by the 
complicated proboscis that is so necessary for the 
sustenance of the Fly ; the compound eyes by which 
we have found the insect races to be characterized 
now make their appearance, as also the delicately- 
constructed feet and wings, and the mysterious 
antennae (PI. VIII. fig. 3). Simultaneously with the 
diAusion, or rather the concentration, of the cylin- 
drical body into head, thorax, and abdomen, a change 
also takes place in the internal anatomy ; for whilst 
this, in the larva, resembled that of the Worm (see 
Letter II.), it now becomes changed to the more 
perfect structure of the Ply, as detailed in the pre- 
ceding letters. In a few days, when all these trans- 
formations are complete, the insect forces its way out 
of its prison-house in the following manner : — After 
it has, by a series of muscular efforts, detached itself 
from the pupal covering, it strikes its head forcibly 
against one end of the case time after time, nntil it 
bursts open, as it were, upon a hinge, like the lid of 
a cylindrical snuff-box (PI. VIII. fig. 4). 

When the Fly first makes its escape, it presents 
anything but a graceful appearance; for, whilst it 
was in the pupa-case, its members were folded against 


72 


HUMBLE CREATURES. 


the lx)dy more with a view to economy of space, than 
to display their elegance; and the wings are neces- 
sarily crumpled and insignificant in appearance. As 
mentioned in the previous letter (VII.), these members 
are supplied internally with a great number of 
trachese, or air-tubes ; and one of the first operations 
of the insect is to inflate these by a trembling motion, 
and by the expansions and contractions of the ab- 
domen : in thus dilating the tracheae, the insect gives 
to the wings their necessary expansion and support. 

We have now followed the Fly from its first ap- 
pearance upon a dunghill, imtil it enters the habita- 
tions of man, and feeds at the tables of monarchs and 
peasants. Of its habits in this, the last phase of its 
history, we can tell you but little that you do not 
already know. Its brief existence presents but few 
facts that are of interest to the naturalist ; for the Fly 
neither constructs dwellings like the bee, nor does it 
display any peculiar instinctive intelligence in its 
natural operations. 

In its perfect form it appears to be as great an 
epicure as it was a gourmand in its larval stage, and 
indulges in all the delicacies of our table whenever 
they come within its reach. It delights to bask in 
the sunshine, but at the first approach of winter re- 
treats into the warm nooks and crannies of our dwell- 
ings, and secretes itself in curtains and drapery ; and 
when the cold sets in, its swarms vanish as rapidly as 
they first made their appearance in spring. 

But even its brief and apparently gay and tranquil 


THE FLY. 


73 


existence is not unattended with danger. That it is 
massacred and poisoned wholesale by man, falling a 
victim to its keen appreciation of the sweets of life ; 
that it is devoured by birds, cats and other qua- 
drupeds, spiders, &c. ; tortured and crushed to death 
by children, and dissected by microscopists, you are 
doubtless Avell aware. But there is another peril to 
which it is subject, and of this you are perhaps not 
cognizant; this is a curious disease to which vast 
numbers fall victims towards the close of the autumn, 
and, although highly interesting to the naturalist and 
microscopist, it must be a fearful infliction to the 
poor little Fly. As this disease has been very gra- 
phically described in a recent number of the ‘ Micro- 
scopic Journal,^ we cannot do better than transcribe 
a short extract*: — 

“The subject of this paper is the well-knoMui 
curious disease which prevails among common House- 
flies at the period when the departing wannth of 
autumn induces them to seek shelter within doors. 

“ At this time innumerable dead bodies of flies may 
be seen adhering to the windows, walls, shutters, &c., 
in all parts of the room : the dead insect, although 
dry, and so friable as to crumble into dust upon the 
slightest touch, retains so far the attitude of life, that 
it is difficult, Avithout touching, to believe that it is 
not a living fly on the point of taking flight. Insects 

* “Empusa Muscae; the Disease of the Common House-fly. 
By Dr. F. Cohn.” Breslau, 1855. — ‘ Microscopic Journal,’ April, 
1857. 

E 


74 


HUMBLE CREATURES. 


in dying usually draw up the legs, and cross them 
beneath the body ; but in the case of the disease now 
under consideration, the dead body is supported upon 
the outstretched legs, whose feet retain their adhesive 
property, and by the protruded proboscis, with which 
the Fly would seem to be sucking; and by which, 
even when the feet may happen to be detached, the 
body is still retained in situ. The dead flies in this 
condition are always surrounded with a halo, about 
an inch in diameter, composed of a whitish dust, 
which upon examination is found to consist of the 
spores [seeds] of a fungus. The abdomen is much 
distended, and the rings composing it are separated 
from each other, the intervals being occupied by white 
prominent zones, constituted of a fungoid growth 
proceeding from the interior of the body. Further 
examination will show that the whole of the contents 
of the body of the Fly have been consumed by the 
parasitic growth, and that nothing remains but an 
empty shell, lined with a thin felt-like layer, com- 
posed of the slender mycelia of the innumerable fungi. 

''This disease appears to have been long' noticed, 
though of course, in the absence of sufficient micro- 
scopic assistance, its true nature was not at first 
known. First noticed it would seem by De Geer, in 
1782 , it did not escape the minute eye of the illus- 
trious Goethe, who gives an accurate description of 
the phenomena attending it, and especially of the 
appearance of the white dust between the rings of the 
body and its dispersion in a wide area around the 


THE FLY. 


75 


dead insect. Accurate microscopic observations were 
made upon it by Nees v. Esenbeck in 1827, though 
he did not arrive at any very definite conclusions as 
to the nature of what he observed. But in 1835 
Mons. Dumeril declared the fine white dust to be 
a true mould, which had probably caused the death of 
the animal, in the same way that plants are killed by 
the difierent species of Eocysiphe : he compares it to 
the ‘ muscardine ’ of the silkworm.” 

With this extract we shall close the life-history of 
the Fly, and shall now consider for a moment the 
uses for which it was created, and the lessons we may 
learn from its existence. 

If you asked a sceptic, who doubted that every 
species of animal is created for an end, and has its 
place and object assigned by the Creator, to name 
some of those that he regarded as useless, it is not at 
all improbable that he Avould select the Worm and 
the Fly. Of the Worm’s value as a fertilizing agent 
we have already spoken (Letter III.), and shall now 
find that the humble Fly, in its lowest stage, per- 
forms an office of still greater importance, — nay, 
that it is indispensable to the existence of some, and 
to the health and comfort of the whole human race. 
Reader ! this is no exaggeration : go into the fields 
or lanes, and seek the body of some recently-killed 
animal ; or, if you reside near the sea, look at the 
carcase of one of the many creatures that are cast up 
by the waves; and if your olfactory organs be not 
too easily offended, turn the body over, and examine 

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HUMBLE CREATURES. 


it for yourfelf. See wlmt myriads of maggots are 
writliing throughout its frame ! A few hundreds of 
these may be the larvae of the Carrion Beetle, or of 
the Devil’s Coaehman {Staphylinidce ) ; but thousands 
upon thousands are the maggots of flies, and, if you 
return a few days after your first inspection, you will 
find that they have devoured the whole carcase, save 
a little skin, and the indigestible bones. The ele- 
ments of the tissues, instead of decomposing into 
poisonous and ill-savoured compounds, and filling the 
air wdth miasma pregnant with pestilential disease 
and death, at once spring phoenix-like into life again, 
and in a few days there appears the animated form of 
the Fly, which only an Omnipotent hand could have 
moulded with such rapidity and accurate design. 
That which was left of the carcase, the bones, form 
one of the most valuable manures that we possess ; 
and whilst the elements of the flesh and tissues rise, 
to form a living creature of the air, the bones descend 
into the earth, and there enter into the constitution 
of plants, and provide nourishment for other animated 
beings. The Fly in its turn falls a victim to birds, 
frogs, or rapacious insects, and these in like manner 
become the prey of man and the lower animals, or 
are converted into the constituents of the soil ; and 
thus it is that the current of life flows on in constant 
and ever-varying circles. 

The history of the Fly also leads our thoughts 
back into the obscure past, even to the earliest periods 
of Creation, and here again it testifies to the wisdom 


THE PLY. 


77 


and omnipotence of the Creator. That the insect 
and its congeners were formed long before man, is 
evident from the circumstance that traces of its fragile 
remains have been discovered far down in the geo- 
logical formations. Then, as now, each mechanical 
portion of its structure was suited to the element 
upon which it operated, or that entered the body of 
which it was to become a constituent part. Then, too, 
its wings propelled it rapidly through the limpid atmo- 
sphere, and its spii’acles sifted the self-same atmo- 
sphere before admitting it into the circulating tubes. 

The insects that formerly existed were cliiefly such 
as were suited to a life in the vast woods and forests, 
and their larvae were developed in the eai-th itself * ; 
but when man received possession of the earth, and, 
in accordance with his Maker^s will, beautified and 
laid it out in gardens, then the Creator altered the 
nature even of the humble Fly, and brought into 
existence new races, adapted in their structure and 
habits to the clianged surface, or produced in greater 
abvmdance the requisite forms, that had before been 
but sparingly distributed f. These revelled amongst 
sweet-scented flowers and herbs, and their young were 
reared upon decaying vegetation. Even in the past 
history of the insignificant Ely, therefore, and in the 
links that have connected it with creation, do we 
read of steadfast unity of purpose, eternal wisdom in 
design, and boundless power in execution. 

* Tlic Nemocera, or long-homed Diptera. 

t The Brachycei'u, or short-homed Diptera. 


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78 


HUMBLE CREATURES. 


And now, dear Reader, we mnst draw these ob- 
servations to a close, and shall claim your attention 
whilst we address a few concluding remarks to you 
concerning the task that we have accomplished. 

If you were pre\'iously unacquainted with the 
nature of the Worm and Fly, we hope that our de- 
scription and history will have revealed to you such 
novel facts as are calculated to elevate your concep- 
tion of these two animals, and invest them with fresh 
interest. We have endeavoured, without burdening 
your mind with scientific details and phraseology , to 
lay before you the principal circumstances that have 
been ascertained in regard to their structure and 
history, up to the present time; to communicate the 
enjoyment afl’orded to ourselves by the investigation 
of the various organs, and thereby induce you to 
take a deeper interest in the subject, and occupy 
yourself Avith inquiries into those functions that you 
Avill have found to be imperfectly understood. It is 
difficult, cither by a description, or plates, to impart 
an adequate idea of the various beauties that present 
themselves in an investigation of the different parts 
of the Fly^s structure with the aid of the microscope ; 
and if these pages lead you to examine for yourself 
the curious mechanisms by Avhich the creatui’e per- 
forms its vital functions, we have little doubt that 
the pleasure you will experience will be to you, as it 
has already been to many others, the magnet that 
will attract you to a more earnest search after scien- 
tific knowledge. 


TUK FLY. 


79 


If you are a scientific student, and have already 
devoted some time to the pursuit, we trust that our 
remarks will have opened new avenues of thought, 
and been suggestive of fresh ideas or subjects for in- 
vestigation. At least, we may confidently hope that 
we have succeeded in accomplishing the object we 
had in ^dew in undertaking this task, and to which 
Ave referred in our Introduction, namely, to display 
those remarkable characteristics in tAvo of the hum- 
blest of animal forms, Avhich render them interesting 
to the naturalist, and to show that the mechanical 
contrivances Avith AA^hich they are supplied are far 
more deservdng of our attention than the instruments 
constructed by the hand of man after their model. 

If Ave have been so far successful, and have rendered 
populai'ly interesting these tAvo creatures, Avhich from 
their very familiarity were considered unworthy of 
notice, Ave shall be well satisfied, and amply repaid 
for our efforts to compile and lay before you this brief 
account of the anatomy and natural history of the 
EartliAvorm and common House-fly. 


FINIS. 



Printed by Taylor and Francis, Red Lion Court, Fleet Street. 



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