Humble creatures; part 1. The earthworm and the common housefly, in eight letters

jumble creatures; By James Samuelson, ass

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Frontispiece

CH Ford

HUMBLE CREATURES;

PART I.

THE EARTHWORM

AND

THE COMMON HOUSEFLY.

IN EIGHT LETTERS.

BY

JAMES SAMUELSON,

ASSISTED BY

J. BRAXTON HICKS, M.D. Lonp., F.LS., &€.

WITH

MICROSCOPIC ILLUSTRATIONS
BY THE AUTHORS.

Post Cenebras Lu.

SECOND EDITION.

LONDON:

JOHN VAN VOORST, PATERNOSTER ROW.

MDCCCLX.
i)

“The bird that soars on highest ae
Builds on the ground her lowly nest ;
And she that doth most sweetly sing,
Sings in the shade when all things rest :—
In lark and nightingale we see
What honour hath humility.”
Montcomery.

PRINTED BY TAYLOR AND FRANCIS,
RED LION COURT, FLEET STREET,

TO

WILLIAM SPENCE, Esgq., F.R.S., F.LS.,

Author of the “INTRODUCTION TO ENTomoLoey,” &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 your own
labours have borne fruits in the minds of others, who,
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 structure of the
eyes, antennee, and internal organization of the insect

races will be found, than have been here presented.

Liverpool, July 1860.

CONTENTS.

LETTER I.

INTRODUCTORY 20... cece eee cece eee eeees Baeaihee page

LETTER II.

The Class “ Vermes” and its subdivision into Orders.—
Lumbricus terrestris, the common Earthworm.—Its Form.
—Members of Locomotion.—Mouth.—Aliment.—Nature
of Worm-Castings.—Digestive Organs.—Circulating Ap-
paratus.—Nervous System .......eceeeerceeeeeseeeeees

LETTER III.

Mode of Reproduction in the Earthworm.—Its Habits.—
Dwelling.—Uses in the Formation of the Surface Soil.—
Conclusion saenere sed eesceseneasinadineeseaieres sisssiere wares

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
Siructite oz.c a aeemisedas thiont sawkw vetoes cs Roeacwiees

LETTER V.

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

tee ee

17

26

vi CONTENTS,

LETTER VI.

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 4

LETTER VIL.

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

LETTER VII.

Life-history of the Fly.—Organs of Reproduction.— Mode of
depositing its Eggs.—Table showing its remarkable Re-
productive Powers.—The Larva; 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 ................005. (

PL.
PL.

Pu.
Pr.

PL.

INDEX TO PLATES.

I. FRONTISPIECE.

Te esc cee gina si orotate saws a aula comage es ore page 8

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

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

Fig. 8. Anterior rings of Worm, with lip, hooks, and
respiratory apertures.—From Burmeister.

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

III. Diagram showing the anatomy of Musca vomitoria 26

Vives lane 2 temiree eal asaiowaes Gare) Meh od Aine ie ass 34
Fig. 1. Head of House-fly, magnified 20 diameters :

a, a, feelers; 6, b, compound eyes; ¢, proboscis.
Fig. 2. Magnified portion of detached cornea.
Fig. 3. Section of part of compound eye.
Fig. 4. Five ocelli, highly magnified.

. V. Proboscis of House-fly ...... 0... cece eee ee eee 43

Fig. 1. Proboscis entire, showing lancets, &c.
Fig. 2. Magnified ribs.
Fig. 3. Magnified section of ribs.

Wile scv oni aa innate e mem o's beaias oe eckbiea ate ee 51
Fig. 1. Section of Fly, showing nervous system, &c. :
a, wing; 6, nervous system.
Fig. 2. Antenna of Fly.
Fig. 2a. Sensory depressions and closed sacs on the
same, highly magnified.

viii INDEX TO PLATES.

Fig. 3. One of the halteres.

Fig. 3.a, 6. Vesicles at the base of the same, highly
magnified.

Fig. 4. Leg of Fly: a, coxa; 6, trochanter; c, femur;
e, tibia; f, tarsus.

Fig. 5. Trachea, or respiratory tube, with coil.

DB, MIG: icsirer cine pest aalels Haggtlasaaienousvessaeweunn page 54

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

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

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

Pu. VIL. (Figures after Griffith.) co... cece cece ee eee 64

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

Fig. la. 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. 5. Anterior extremity of larva, with palps retracted.

Fig. 6. Anterior extremity of larva, with the same ex-
panded, showing also the trachee and rudi-
mentary feet.

THE EARTHWORM

AND

THE COMMON HOUSEPFLY.

—_>—_

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 works 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 observer, we find them
to be so wisely constituted, and to possess such in-
teresting appliances by which they perform their
natural functions, that we begin to wonder how it is
we should have remained so long in ignorance of
their remarkable properties. We find ourselves in a
new world, and the objects contained therein, at the
same time that they impart sensations quite as plea-

INTRODUCTORY. 3

surable as those which were wont to excite our childish
imaginations when first we beheld 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 we 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 whose 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 will not fail to
convince you that there is considerable enjoyment
connected with the study.

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

B2

4 HUMBLE CREATURES.

another, who 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 you 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 other, 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 (Pl. II. fig. 2).

It has perhaps never occurred to you to inquire
how it is, when you 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 disappears 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. 5

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 we 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 wit-
nessing a strange, and, to the masses, inexplicable
phenomenon connected with the insect, namely the
mode in which it walks upon the ceiling with its feet
upwards, or progresses upon the smooth vertical pane
of glass in your parlour window, setting at defiance a
well-known law of gravitation. If you are not able
to solve this mystery, ask some friend who possesses
a microscope to show you the foot of a fly under the
instrument, and you will find, that at its extremity it
is furnished with a pair of membranous discs, on
which there are disposed countless minute suckers,
that operate upon the inverted céiling, or smooth
glazed surface over which the fly is marching, in the
same manner as did the leather sucker with which, as
a schoolboy, you were wont to amuse yourself in
liftmg heavy stones: this is the simple, but effective
apparatus which enables the little creature to main-.

6 HUMBLE CREATURES.

tain its hold with security in any position (Pl. VII.
figs. 1 & 1a).

Nay, you may even, whilst lounging lazily upon
your sofa, watch some little fly that has settled upon
your coat, and is busily engaged in removing the dust
from its wings: you will 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
with 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 msect ; 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 structure of the worm and the fly, may have
awakened 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 purposes; and we hope that you may now
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 les in our power, to make you acquainted
with 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 who have devoted their attention to the sub-
ject, and of such of their works as we 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 view of the subject.

8 HUMBLE CREATURES.

LETTER II.

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

Few persons have a correct 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 which 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)

CLASS VERMES. 9

external hardened cases, as in the beetle and other
insect tribes; nor yet a calcareous shell, as in the
univalve or bivalve mollusks, such as the snail
and oyster. With few exceptions, their bodies are
unprotected by any kind of hardened envelope, and
they possess no articulated 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 worms, 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 the Ascaris and Strongylus,
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 Platyelmia, or
flat worms, is more numerous than the last. In some
cases, as in the Cestoid worms (e.g. the Tenia, or

* Vogt, Zoologische Briefe. Frankfort, 1851—Carpenter,
The Microscope. London, 1856.—See also Burmeister’s Zoolo-
gical Atlas. Berlin, 1843.—Achille Richard Eléments d’Hi-
stoire naturelle. Paris, 1849.

BS

10 HUMBLE CREATURES.

common Tapeworm), the body is divided into a grea
number of segments, all similarly formed and or.
ganized ; in others, as in the Planarian worms, inha.
biting the water, it consists of one flattened, undividec
disc. ‘These are two of the great variety of group:
aud families which comprise the order.

3. The third order is wholly microscopic. They
are termed the Rofifera, or wheel-bearing worms
are found in incalculable numbers in fresh and salt
water, aud 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 worms, 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 are found on the sea-shore, and
construct for themselves tubular dwellings; the Nais
or Mud-worm; and the “ Hrrantia’” or “ Natantia”
(errant, or swimming worms), 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. 1]

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

The Annelida, or annulose worms, then, the highest
and most perfect of the four orders, contain amongst
their number the Earthworm (Luméricus terrestris),
which, in common with its congeners, possesses, as
you well know, a soft elongated body. This, in the
full-grown animal, is usually divided 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, we have already alluded
in our Introduction, and these are the only append-
ages that the worm possesses (see section of Worm’s
body, Pl. II. fig. 4). But you will perhaps be some-
what surprised to hear us speak of the “head” of
a worm, for you are accustomed to connect with that
idea a mouth, eyes, nose, and ears, none of which
are perceptible in the worm; and the first, that is the
mouth only, being actually present. Although, how-
ever, the senses of vision, smell, and hearing are, so
far as we have 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 with 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 smalle:
or lower lip is placed in juxtaposition.

These two lips form an imperfect ring, and consti
tute the oral aperture or mouth, which is howeve:
not provided with teeth, nor organs of any othe:
description. This being the case, and as the worn
possesses no prehensile members with which to lay
hold of its food, you will naturally be curious to knoy
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*. A:
least you will say, this diet cannot be very indigest.
ible; but we fear you will smile incredulously wher
informed that the Earthworm not only inhabits thi
earth, but also feeds upon the element in which 1
exists; and although some naturalists have declarec
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. Thi
soil is, as you will probably be aware, impregnatec
with decaying organic substances of various kinds
and im 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 ic
enabled to seize by darting forth its wonderfully constructe¢
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 whole
length with a granular envelope, composed of nu-
merous glands, which 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 through 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 will perceive the return current flowing in the
opposite direction, through 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.

extent of the nature of that organ in the higher ani-
mals, inasmuch as its wall, or limitary membrane, is
elastic, and by its contractions propels the blood on-
wards. Whilst 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 united to the former by a
number of smaller veins into which the blood also
penetrates, so that it may yield its regenerating con-
stituents to every portion of the body.

The aération 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 beimg 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 we shall consider in a subsequent letter, we

THE EARTHWORM. 15

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

This is framed in conformity with the general shape
of its body, and is as simple as the organs already
described. It consists, first, of a minute roundish
mass of nervous substance, termed the “cephalic
ganglion,” which 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 throat (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 excru-
ciating pain the angler inflicts 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—worms, millipedes, crustaceans,
arachnide, and insects,—the central nervous 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 III.

MODE OF REPRODUCTION IN THE EARTHWORM.—ITS HABITS.
—DWELLING.—USES IN THE FORMATION OF THE SURFACE-
SOIL.—CONCLUSION.

In our last letter we reviewed cursorily the chief por-
tions of the Worm’s anatomy, and must now devote
a short space to the consideration of its organs and
mode of reproduction.

The worm, in common with many others of the
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 which serves 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 (Pl. II. fig. 2),
situated at about the anterior third of the body, be-
come enlarged, and this swelling, which you will

18 HUMBLE CREATURES.

doubtless often have noticed, strongly resembles a
healing wound, for which it is usually mistaken by
the uninitiated. From this portion of the body a
glutinous substance, secreted by special glands, ex-
udes; and although, as just observed, the worm is
hermaphrodite, yet contact with another of its species
being necessary 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 (Pl. IL
fig.1). 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 born 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
will 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 underground? Its dwelling consists of
one or more burrows, of the same shape as its body,
which it constructs 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. 593.

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 we alluded to in a former
letter under the designation of “ worm-castings.”
We shall narrate briefly how this interesting circum-
stance was first discovered, showing at the same time
how important a part the worm plays in the con-
struction and fertilization of the soil.

About twenty years since, an eminent naturalist*,
whilst visiting a friend in the country, was surprised
to hear from his host, that on some pasture-land
which he possessed, an unaccountable change had
taken place in the character of the soil, which in
various fields had, without apparent cause, materially
increased in depth during the previous years, and
that cinders and other substances, which 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. 505; his paper “On the Formation of Mould.”

THE EARTHWORM. 21

in these he found similar indications 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 the language of farmers who are acquainted with
these facts) the fragments had * worked themselves
down.’ It is, however, scarcely possible that cinders
or pebbles, and still less powdered quicklime, could
sink through 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 the blades of grass in the fields above
described, I found scarcely a space of two inches
square without 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.

their form until 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 averse 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 34 inches had been weil 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 well 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
conclusion may appear at first startling, it will 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 concludes by remarking,
“that the agriculturist, in ploughing the ground,
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
principle to which we have more than once alluded
in the course 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 words 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 worm) still more humble Madrepore polyp,
commonly known as the Coral insect; how m the
course of ages it bulds up continents in the midst of
the ocean; will not for an instant be inclined to doubt
that the worm aids in the deposition of the surface-
soil, simply on the score of its apparent insignifi-

24, HUMBLE CREATURES.

cance; and although the traces of the Annelide 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 polyp just
referred to) pursued 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 mould, a circumstance which we believe
to be placed beyond a doubt ; still our assertion holds
good, that its history affords 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 afford 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 with 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 him in his
sport as a requital for the services 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.

26 HUMBLE CREATURES.

LETTER IV.

CUVIER’S CLASSIFICATION OF ANNELIDES 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 FLY’S FORM AND STRUCTURE.

Oy 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

Scales coverng Halteres

Pulmonary Sac

Intestinal Cenal --

Compound Eye

Large Respiratory Trachea

Pulmonary Sac

- Abdominal Trachea

Cloaca

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 all a scientific know-
ledge of zoology, are well aware that each great 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 ‘“ Annulosa,” 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 unites the Annelides (of which the Earthworm is
the typical 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 which induced us to couple the Worm and the
Fly in one treatise.—(See page 10, Letter II. “ Natantia.”)

c2

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 structure before they assume their cha-
racteristic type.

Let us take, for example, the two groups of which
we are here treating, namely the Annelides 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 furnished with no external
members except the rows of hooks that serve to aid
them in locomotion; but 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 difference 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
Articalate type is going on; first the legs and then
the wings becoming developed; and when the meta-
morphosis is complete, the insect bursts its prison-
house and issues forth in its perfect or ‘imago’ form,
furnished with legs and wings, and all those wonder-
ful appliances, which we shall presently describe in
detail.

The foregoing comparison will show you, that not
only the outward forms of animals, but also their life-
history, and the metamorphoses to which they are
subject, are all duly considered by scientific zoo-
logists, in their systematic classification. But the
knowledge of this fact is all that need be deemed
essential for our purpose ; for we are not dealing with
groups, nor even genera, but only with species ; and it
matters very little to us whether zoologists have
placed the Earthworm at the head of one group, of
which 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 per 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 fully developed insect
(imago), although in the larval stage the number of
these members is arbitrary, varying in the different
groups; and even in some cases they are entirely
absent. Another, although not so constant an attri-
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 three 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 undergo 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. 3]

maturity. Of this group, which is but limited, the
Louse (Pediculus) is a well-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 (Acridium), the Dragon-
fly (Lidellula), and that terror of all good housewives,
the Bug (Cimez).

Lastly, we have an extensive race of insects that
undergo a complete transformation (Holometabola), 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 all 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 (Vespa), the Butterfly (Papilio),
the Beetle tribes (Coleoptera), and, amongst many
other similar forms, the common House-fly (Zusca do-
mestica), are all members of this extensive group.

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 province 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 unassuming as its form may
appear to the superficial observer, it has been deemed
worthy of a large share of the zoologist’s notice ; 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 referred
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.

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

THE FLY. 33

or brain, and the nerves of sense proceeding there-
from to the organs just named.

2. The thorax, or chest, is again subdivided into
three parts ;—imperfect rings, the anterior of which
is termed the prothorazr, the middle the mesothoraz,
and the posterior the metathorav. On these three
rings the members of locomotion are distributed as
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
PL. 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,
cb

34 HUMBLE CREATURES.

LETTER V.

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

TuereE 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
will find in front of the forehead a pair of short
antenne or feelers (Pl. IV. fig. 1, a, @), organs which,
in some of the insect races, impart those wonderful
instinctive properties that have in this respect raised
their possessors to a level with the so-called higher
animals, and have rendered them a complete mystery
to the naturalist.

The antenne 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 (Pl. 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.

When the fly is at rest, the first three jomts lie in
a depression of the insect’s head (Pl. IV. fig. 1, a, a),
whilst the plumose joint is seen to protrude: the

CH Fard Lith,

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 antennze is, that the third jomt, when mag-
nified, is found to be perforated all over with minute
punctures ; these are in reality (as a high magnifying
power reveals, after the antenna 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 (Pl. VI. fig.2,a). Near the base of
the joint are three or four larger apertures leading into
chambered cavities, protected at the bottom by micro-
scopic hairs, and to each of these cavities 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
antenne ? 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 superadded to the
latter sense that of touch.

These conclusions have been arrived at by com-
paring the structure of the antennze 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 adduced, as an in-
stance where the feelers exhibit a sensibility to sound,
the fact of a beetle, which retracts its antenne on a
sudden noise, and falling down counterfeits death.
On the other hand, we have various circumstances in
evidence of their tactile 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 larve of various insects; ou the
bodies of these, the larve of the Ichneumon subsist as
soon as they are hatched. If we observe this insect
secking for larvee or caterpillars that inhabit wood,
old posts, &c., we shall notice that it pushes its an-
tennz 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 antenne 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, whose larve 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 larvee, in consequence of which they
died of hunger almost as soon as they were hatched.
The Bee, again, employs its antenne, 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 antenne. 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 +.

If the antenne of the Fly have proved a mystery to
naturalists, equally so have its wonderful eyes been
the subjects of speculative inquiry. These are five in
number, two being compound, and of comparatively
enormous proportions ; for they monopolize the greater
part of the head, from each side of which they pro-
trude in a semi-globular form (Pl. IV. fig. 1, 04).

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

+ The sense of hearing has been assigned to them by Bur-
meister, Carus, Strauss-Durkheim, Oken, Robineau, Desvoidy,

and Newport; that of smell, or smell and touch, by Reaumur,
Lyonnais, and several French anatomists, Kiister, Erichson, and
Vogt.

It appears to us, that if insects, whose sensibility to external
influence is known to be acute, were confined and watched,
fresh light would be thrown upon the nature of their antenna.

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 (Pl. 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 (P1. 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*. Hach pyramid
is imbedded in a dark pigment; so that the light
which enters one facet may not be dispersed, nor

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

THE FLY. 39

penetrate into the neighbouring one, and thus cause
a confusion of rays; from each facet, or rather from
the apex of each pyramid, a distinct nerve passes into
the substance of the eye, and all these nerves meeting
in one common centre, form a large nervous trunk,
which conveys the image of surrounding 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 which 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
multiplying-glass, which is a prism of many facets.
It has, however, of late been shown that such is not
necessarily the case; for, although it can be clearly
demonstrated that each facet receives 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, but only one distinct image is apparent to
our sense. A still more remarkable example of the
fusion of images is, however, found 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 still
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 necessary before we can
regard this as an established fact*.

Probably the existence of the compound eyes may
be attributed to the circumstance that insects seek
their food in the deep tubes, or dim hollows of flowers,
and have frequent occasion to enter crevices into
which the light but partially penetrates. A single
image reflected in such localities would be faint and
“imperfect ; whereas a series, collected, as we 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 were employed in the minute eyes of
insects, as concentrates the external rays in our own
organs of vision, we mean the contractile iris, the
disposable surface would be almost entirely absorbed,
and little room left for the admission of rays; whilst
it appears much more natural and in accordance with
the general structure of insects (which affords nume-
rous examples of a repetition of similar parts), that
they should possess a number of simple lenses, than
that the visual organs should be furnished with the
mechanical contrivances attached to those of the
higher animals. If this be so, we may say with
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 ina
similar manner from the other set of eyes in another insect,
and observe the result. The comparison of the movements in
the two cases led to the above conclusion.

42 HUMBLE CREATURES,

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

* The Fly is furnished with . . . 4,000 facets.
The Mordella (a kind of oe 25,000 facets.
The Dragon-fly. . . . . . 12,544 facets.
The Butterfly . . . . . . . 17,355 facets.
The Sphinx Moth. . . . . . 1,800 facets. ‘
HS EATIE 4 a se ciao eel. Se oa 50 facets.

(Burmeister.)

PLATE V.

Proboscis

THE FLY. 43

LETTER VI.

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.—REPE-
TITION OF SIMILAR PARTS IN THE ORGANS DESCRIBED,

Berore passing from the consideration of the Fly’s
head, we have still to examine another organ, namely
that of nutrition, which is termed the prodoscis; this
is situated in front, towards the under surface 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 ¢ypical struc-
ture of the mouth of insects generally. Those that
masticate their food are usually furnished with the
following parts:—1. an upper lip (/abrum), and a
lower lip (Jabiwm), 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 (mandibule), and, 3. a smaller pair (maz-
ille), which operate laterally and masticate the food ;
and, 4. we find two pairs of feelers; the first (mawi/-

44, HUMBLE CREATURES.

lary palpi) attached to the maxille, and the second
(palpi labiales) connected with 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 wanting, and a proboscis or suction-
pump is substituted, as being better adapted to the
changed character of the food on which the insect
subsists. On examining it more closely, however, we
find that the proboscis is, after all, but a transforma-
tion of the maxillary organs just referred to as exist-
ing in the generality of insects. Let us take that of
the House-fly for example. The proboscis of the Fly
(Pl. IV. fig. 1, c, and Pl. V. fig. 1) consists of a tubu-
lar bag, formed of thin transparent membrane, which
arises from 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 lower 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 (Pl. V. fig. 1, a) is so constructed as to
gather the fluids and attract them towards an aper-
ture at 6, which 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 (4). The apex of the latteris

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 ‘maxille’ 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 from the circumference to the centre, as in
Pl. V. fig. 1,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 Pl. 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 (¢rachee), 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, antennz,
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}, suffices to show their structure; and if
you desire to become acquainted with the physiology
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 division
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,
one 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
served to illustrate this treatise were prepared by Mr. Purkiss
of Tottenham.

+ A microscope may be purchased for 10s. 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 chest.

The most important of these members, looking at
the habitat of the Fly, are undoubtedly the wings.
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 layers the blood-vessels and respiratory
tubes (¢rachee) 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 intervening 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 fully 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 this treatise, we
must not omit to refer to the remarkable effects that
they produce, and will dwell for a moment upon their
wonderful 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 also 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 carry it 5 feet, every second; but if alarmed,”

THE FLY, 49

he states, “their velocity can be increased six- or
seven-fold, or to 30 or 35 feet per second. In this space
of time a race-horse would clear only 90 feet, which is
at the rate of more than a mile per minute. Our little
Fly, in her swiftest flight, will in the same space of
time go more than the third of a mile. Now, compare
the infinite 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-train. Though this may ap-
pear exaggerated, the calculation will not seem so far
from the truth, when we notice that, whilst 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 (Culea pipiens)
has a much higher rate of vibrations, which are com-
puted at many thousands per second.

' In such insects as possess two pairs of wings, e.g.
D

50 HUMBLE CREATURES.

the Butterfly, Beetle, Dragon-fly, &c., the second pair
is situated upon the metathorax, the third rig; but
in the Fly, which is only furnished with one pair, the
place of the second is supplied by two little members
termed halteres, or poisers. These appear to be rudi-
mentary wings, are 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 (Pl. 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 antenne,
numerous hairs are interspersed with great regularity.
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 ¢o 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
antennee, in which the vesicles are depressed, as stated

* Mr. Purkiss and Dr. J. B. Hicks: see papers by latter in the

Jounal of the Linnean Society, vol. i. No.3; and Linnean
Society Transactions, vol. xxii. p. 144.

THE FLY. 51

in a former letter; whilst those in the halteres and
wings project from the surface (Pl. VI. fig. 3, and b),
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 (Pl. VI.
fig. 4, a); then the “ trochanter,” a short round
joint (Pl. VI. fig. 4, 6) ; next the “femur,” or thigh,
the largest of the five joints (4, c); the “ tibia,” a
somewhat thinner member (4, d); and lastly, the
“tarsus,” or foot (4,f). None of these are distin-
guished by any feature of peculiar interest, excepting
the last-named; but that one we shall find quite de-
serving 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
polished surfaces, and also to progress in a position
opposed to the laws of gravity.

This apparatus consists of two moveable claws
(Pl. VII. fig. 1), resembling a cow’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

D2

52 HUMBLE CREATURES,

(same figure), resemble the broad termination of a
child’s battledore formed of parchment. Until re-
cently, these pulvilli, 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
(Pl. VIT. fig. 1, a) serves as a sucking disc, the two
pulvilli 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 ambulacral suckers that serve as members of
locomotion in the Star-fishes and other Echinoderms,
and the terminal cushions upon the toes of the Climb-
ing-frog (Hyla arborea), in all of which a power is
imparted similar to that possessed by the House-fly.

With this description of the Fly’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 antenne, wings, and halteres with their
numerous vesicles, and lastly, the pulvilli with the
appended suckers, all present examples of that pecu-
larity 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, will doubtless soon clear up the
mystery ; and should you be inclined to enter the
ranks of observers, you will find the field to be one of
unbounded study and interest.

54 HUMBLE CREATURES.

LETTER VII.

THE ANATOMY OF THE FLY.—ITS ORGANS OF DIGESTION; OF
CIRCULATION; OF RESPIRATION.—WONDERFUL STRUCTURE
OF THE SPIRACLES OR BREATHING-HOLES, AND TRACHEE
OR RESPIRATORY TUBES.—NERVOUS SYSTEM.—CONSIDERA-
TIONS UPON THE NERVOUS SYSTEM OF THE HOUSE-FLY
AS COMPARED WITH THAT OF ITS LARVA AND OF 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 aérial existence; and if
we now investigate its internal structure, we shall sce
that the vital organs are 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*.

* Léon Dufour, Anatomie Générale des Diptéres, Ann. des
Sci. Nat. i. p. 244; Vogt, Zoologische Briefe, vol. i. p. 598.

CBN ant, lit

THE FLY. 55

From this crop the food passes into an extended
stomach, and thence into a long convoluted bowel, 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 commencing 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 articulate
series, we have here four distinct divisions in the di-
gestive apparatus,—a progressive step in the develop-
ment, with which we shall find the other vital organs
in perfect accordance. In regard to the circulation of
the blood, for instance, you will recollect that the
Worm possessed one undivided contractile tube, which
extended along the back, and, performing 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 (PI. ITI.) 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, known 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. 57

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 will 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 will 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

vs)

58 HUMBLE CREATURES.

beautifully constructed organs, the air passes into
fine tubes called trachea, 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 insect’s
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 aperture
there proceed towards the centre a great number of
short arborescent trunks (Pl. 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 trachee 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 the circulation of
the air is then arrested; and unless some means were
employed to re-open the tube, its linimg 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 trachee 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 (Pl. VI. fig. 5) adds considerably to the elasticity
of the air-vessels; and when these collapse through
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 pressure is
removed.

In the distribution of the trachez we find the same
wise arrangement that characterizes every other por-
tion of the internal economy of the Fly. The addo-
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 (Pl. III.), as well
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.

vided internally with a pair of lateral tubes; in both
cases the main trachez give out innumerable minor
branches, 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 structure (Pl. VI. fig. 1, 6 4)
consists—1l, of the drain, otherwise termed the
cephalic or supra-esophageal ganglion, which is com-
posed of two small masses of nervous matter situated
(as the foregoing expressions denote) in the head,
“above the cesophagus” 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-
esophageal 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 nerves are given off
in pairs (see Pl. VI. fig. 1, 4 8) in all directions, viz.

THE FLY. 61

a pair to the anterior legs, another to the wings, a
third pair to the second 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 (arranged 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 larval 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 found bilateral
branches proceeding from the central chord; and
these branches being often repeated, and of a uni-
form size, afford 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 which 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 the central chord, a nervous ganglion, from
which bilateral branches proceed 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 structures 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 subcesophageal
ganglion. The nerves, too, differ considerably in their
proportions, owing to the unequal development of the
organs and members to which they proceed. The
optic, which has already been described, is enormously
developed, to supply the numerous facets of the com-
pound eye, Next in size is that which proceeds to
the halteres, then that to the wings, whereby the
importance of these organs is sufficiently indicated ;
and the remaining nerves are of comparatively small
dimensions.

We have thus dwelt upon the nervous 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 whole 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 life-history.

64 HUMBLE CREATURES.

LETTER VIII.

LIFE-HISTORY OF THE FLY.—ORGANS OF REPRODUCTION.—
MODE OF DEPOSITING ITS EGGS.—TABLE SHOWING ITS RE-
MARKABLE REPRODUCTIVE POWERS.—THE LARVA; THE
PUPA. — TRANSFORMATIONS. — THE PERFECT FLY; ITS
HABITS.—STRANGE FATAL DISEASE TO WHICH IT IS SUB-
JECT.—ITS USES AS A SANATORY AGENT, ETC.—TRANS-
FORMATION OF 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, still 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.

Hig 1.

fig 2

Rig 5

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 which, 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 feet ;” 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 és 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
Worm; 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).

66 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 larvee, as, for example, the heaps of vegetables
and other substances that are found in the neigh-
bourhood of our dwellings.

“Tf” 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 will 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 cause eggs and larvee 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 moving
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, without causing
her to exhibit the least symptom of alarm. 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
insécts 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 was
completed, and he, as well 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
weeks 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 drawn up the following curious
table, from which it would appear that a single female
might in one season be the progenitrix of upwards of
two million flies :—

68 HUMBLE CREATURES.

“The parent Fly lays her eggs four times
during the summer, and each time she
deposits 80 eges, making . . : 820 flies,
Now, it must be assumed that half of —
are females, so that at each of the four
depositions 40 females are born :—
(1) The first eighth, or the 40 females re-
sulting from the first deposition, lay
again four times during the season,
making together . . ‘ 12,800 ,,
Again, the first eighth of élie86, or 1600
females, deposit three times, making. 384,000 _,,
The second eighth, or 1600 ani de-

posit twice, making . . 256,000,
The third and fourth Swicttis, or * 3200,
deposit once, making . . 256,000 __,,

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

first deposition, ae three times more,
making .. 9,600 ,,

Ghe.aeth of ‘hess, or "1600 derma, de
posit again three times, making . . 384,000 ,,

The second one-sixth, or 1600 females,
deposit again twice, making. 256,000 ,,

The third one-sixth, or 1600 Epics
deposit again once, making. . . . 128,000 ,,

(8) The third eighth of the first laying, or
40 females, lay twice, making . . . 6,400 ,,

Of these, one-fourth, or 1600 females,
deposit twice, making . . 256,000 ,,

(4) The fourth one-eighth of the rat Benes

sition, say 40 females, deposit once

more, making . . 3 3,200 ,,
Whereof one-half, say 1600 faniilea, ae
posit at least once,making . . . . 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 foregSing 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 larve 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 (Pl. VIII. fig. 1 & 1, a) is
divided into thirteen rings, of which the anterior, or
head, is furnished with a pair of hooked jaws, and
curious globular palpi (Pl. VIII. fig. 4), and the-
second bears a pair of rudimentary feet (fig. 1 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 Schwammerdam counted 140 eggs in the body of one Fly.

70 HUMBLE CREATURES.

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

On the posterior portion of the last ring (fig. 1 a, 18),
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 trachee or
respiratory tubes, two or three of which are visible
in fig. 6, ¢, and which serve to aérate 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
(Pl. 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 brown
and tough, inclosing the larva in a little bright
barrel-shaped case, divided into rings or segments
(Pl. 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
antenne (Pl. VIII. fig. 3). Simultaneously with the
division, 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 Fly, 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, until it
bursts open, as it were, upon a hinge, like the lid of
a cylindrical snuff-box (Pl. 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 body 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
tracheze, 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 trachez, 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, until 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 well 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-known
curious disease which prevails among common House-
flies at the period when the departing warmth 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, without touching, to believe that it is
not a living fly on the point of taking flight. Insects

* «“Empusa Musce ; 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. Duméril 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 different species of Exysiphe: 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 would select the Worm and
the Fly. Of the Worm’s value as a fertilizing agent
we have already spoken (Letter ITI.), 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

E2

76 HUMBLE CREATURES.

it for yourfelf. See what myriads of maggots are
writhing throughout its frame! A few hundreds of
these may be the larve of the Carrion Beetle, or of
the Devil’s Coachman (Staphylinide) ; 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 with 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 FLY. 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 spiracles sifted the self-same atmo-
sphere before admitting it into the circulating tubes.

The insects that formerly existed were chiefly such
as were suited to a life in the vast woods and forests,
and their larvee were developed in the earth 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 changed surface, or produced in greater
abundance the requisite forms, that had before been
but sparingly distributed +. These revelled amongst
sweet-scented flowers and herbs, and their young were
reared upon decaying vegetation. Even in the past
history of the insignificant Fly, 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.

* The Nemocera, or long-horned Diptera.

+ The Brachycera, or short-horned Diptera.
FP

78 HUMBLE CREATURES.

And now, dear Reader, we must 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 previously 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 afforded to ourselves by the investigation
of the various organs, and thereby induce you to
take a deeper interest in the subject, and occupy
yourself with inquiries into those functions that you
will have found to be imperfectly understood. It is
difficult, either 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 which the creature 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.

THE 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 view in undertaking this task, and to which
we referred in our Introduction, namely, to display
those remarkable characteristics in two of the hum-
blest of animal forms, which render them interesting
to the naturalist, and to show that the mechanical
contrivances with which they are supplied are far
more deserving of our attention than the instruments
constructed by the hand of man after their model.

If we have been so far successful, and have rendered
popularly interesting these two creatures, which from
their very familiarity were considered unworthy of
notice, we 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
Earthworm and common House-fly.

FINIS.

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

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