ENTOM 
this violent diftenfion, andceafing toaft, the Ikin wrinkles 
and dries up ; at length it opens, and the infeft conies 
forth with a new (kin, and new organs. When we have 
thus formed the idea that all the exterior parts are inlaid, 
or included one within the other, the produdtion of new 
organs does not appear fo embarrafling, being nothing 
more than a fimple developernent; but it is more difficult 
to form any conception of the changes that happen in the 
vifcera before and after the transformation, the various 
modifications they undergo eluding our refeaches. We 
have already obferved, that a little before the change 
the caterpillar rejects the membrane that lines the intef- 
tinul bag : this bowel has hitherto digefted only grofs 
food, whereas it muft hereafter digefl that which is very 
delicate: a fluid that circulates in the caterpillar from 
the hind part towards the head, circulates a contrary way 
after transformation. Now if this inverfion is as real as 
obfervation feems to indicate, how amazing the change 
the interior parts of the animal mull have undergone ! 
To give the curious reader a competent idea of the ad¬ 
mirable ftrudture of the mufcles and interior mechanifm 
of the caterpillar, we have, in the Entomology Plate II. 
fig. i, exhibited an anatomical fedlion of the caterpillar 
of the Phalaena coffus, or goat-moth, eonfiderably mag¬ 
nified to fliew out its parts. The body of this caterpillar, 
and of infedts in general, includes four principal vifcera ; 
the fpinal marrow, the inteflinal bag, the heart, and tra¬ 
cheal veflels. The fpinal marrow, or principal trunk of 
the nerves of infedts, is a whitilh thread, extended the 
whole length from the head to the hindermoll part, fur- 
nilhed at intervals with fmall knots or ganglions. From 
thefe knots proceed the nervous threads that are fuppofed 
to be the inftruments of fenfation and motion. On the 
medullary thread is placed the inteflinal bag, which is 
equal to it in length ; it is a long gut, in which are con¬ 
tained the oefophagus, the Ilomach, and inteflines. Down 
the back, and parallel to the inteflinal bag, runs a long 
thin veffel, in which may be perceived through the fkin 
of the inf'edl alternate contradljons and dilatations; this 
part is fuppofed to perform the functions of the heart. 
The tracheal veflels of infedls are very fimilar to thole of 
plants; are of the fame ftrudlure, colour, and ehiflicity, 
and are, like them, difperfed through the whole body. 
The internal ftrudlure of the caterpillar, as represented 
in the Plate, divides itfelf into twelve parts, correfponding 
to its twelve rings. Each of thefe rings is diflinguifhed 
from that which follows, and that preceding it, by a kind 
of neck, or fmaUc hollow part or fedlion. By conceiving 
a line to pafs through thefe necks, and forming boundaries 
to the rings, the divifions become more apparent. 
The anatomical delineation of the mufcles of the head; 
the two palpi ; the truncated mufcles of the lower lip, 
and part of thofe w'hich give it motion ; the two gang¬ 
lions of the neck united ; the two filk veflels which form 
tubes from the right and left, and pafs through the center 
of the head ; the cefophagus ; the two dilfolving vef- 
iels ; the cephalic arteries ; the ten abdudlor mufcles of 
the jaw ; the four occipital mufcles ; alfo a nerve of the 
ifirft pair, belonging to the ganglion of the neck, may be 
cafily traced by contemplating the engraving. 
The mufcles of the body of infedls have neither the 
exterior form, nor the colour, of thofe of larger animals. 
In their natural flate they are foft, and have the appear¬ 
ance of a jelly ; they are of a greyilh blue, and the filver- 
coloured appearance of the pulmonary veflels, which 
creep over and penetrate their fubflance, exhibirs under 
the microfcope a moft beautiful fpedlacle. When the 
caterpillar has been foaked for fome time in fpirit of wine, 
they lofe their elallicity and tranfparency, and become 
firm, opake, and white; the aerial veflels difappear. At 
fir ft fight they might be taken for tendons, as they are of 
the fame colour, and poffefs almofl: the fame luftre. They 
are generally flat, and of an equal (ize throughout ; the 
middle feldom differs either in colour, fubflance, or fize, 
O L O G Y. 839 
from the extremities. The ends are fixed to the fkin ; 
the reft of the mufcle is generally free and floating ; fe- 
veral of them branch out eonfiderably ; the'branches ex¬ 
tend fometimes fo far, that it is not always eafy to dif- 
cover whether th'ey are diftindt and feparate mufcles, or 
parts of another. They are of a moderate ftrength ; 
thofe that have been foaked in fpirit of wine, when exa¬ 
mined by the microfcope, will be found to be covered 
with a membrane which may be feparated from them; 
they then appear to confift of feveral parallel bands, dil- 
pofed according to the length of the mufcle. Thefe, 
when divided by the affiftance of very fine needles, ap¬ 
pear to be compofed of fti 11 fmaller bundles of fibres, in 
the fame diredlion; which, when examined by a very 
deep magnifier, and in a favourable light, appear twilled 
like a fmall cord. If the mufcles are feparated by means 
of very fine needles, in a drop of fome fluid, we find that 
they are not only compofed of fibres, membranes, and 
aerial velfels, but alfo of nerves; and, from the drops of 
oil that may be feen floating on the fluid, that they are 
alfo furnilhed with many undtuous particles. The muf¬ 
cles in the caterpillar are very numerous, exceeding by 
much thofe of the human body. They occupy the 
greateft part of the head ; there is an amazing number at 
the oefophagus, the inteflines, &c. the Ikin is as it were 
lined by different beds of them, placed one over the 
other, and ranged with wonderful fymmetry. The num¬ 
ber of mufcles is truly aftonifliing; there are 228 in the 
head, 1647 in the body, and 2066 in the inteflinal tube, 
making in all 3941 ! 
The fpinal marrow and the brain of the caterpillar, 
feem to have very little relation to thofe of man. We 
find in the head of that which we are deferibing, a part 
which feems to anfwer the purpofe of the brain, becaufe 
the nerves that are dilfeminated through the head are 
derived from it; but then this part is unprotected, and 
fo fmall, that it does not occupy one-fifth part of the 
head; the furface is fmooth, and has neither lobes nor 
anfradltioufnefs ; and if we call this a brain, the cater¬ 
pillar may be faid to have thirteen, as there are twelve 
more fuch parts following eacli other in a line ; they are 
nearly of the fame fize with that in the head, and of the 
fame fubflance ; and it is from them that the nerves are 
diftributed through the whole body. Left the idea of 
thirteen brains might appear abfurd, M. Lyonet has 
called thefe parts ganglions. The fpinal marrow in the 
human fpecies defeends down the back, inclofed in a bony 
cafe ; is large with refpedt to its length, and not divided 
into branches, diminifhing in thicknefs in proportion as 
it is removed further from the brain. In the caterpillar, 
the fpinal marrow goes along the belly, is not inclofed in 
any tube, is very fmall, forks out at intervals, and is 
nearly of the fame thicknefs throughout, except at the 
ganglions. The fubflance of the fpinal marrow, and of 
the ganglions, is not near fo tender and eafily feparated as 
in man ; it has a very great degree of tenacity, and does 
not break without confiderable tenlion. The fubflance 
of the ganglions differs from that of the fpinal marrow, 
as no veflels can be difeovered in the latter, whereas the 
former are full of very delicate ones. The Ikilful ana- 
tomift of the caterpillar has counted forty-five pair of 
nerves, and two Angle ones ; fo that there are ninety-two 
principal nerves, whofe ramifications are innumerable. 
The tracheal arteries of the caterpillar are two large 
elaftic veflels, which, with their numerous ramifications 
may be prefled clofe together, and drawn out eonfiderably, 
but return immediately to their ufual fize when the ten- 
fion ceafes; they creep under the Ikin clofe to the fpira- 
cula, one at the right fide of the infedt, the other at the 
left, each of them communicating with the atmofphere, 
by means of nine fpiracula ; they are nearly as long as 
the body, beginning at tlie firft ipiraculum, and going a 
little farther than the laft, terminating in fome branches 
which extend to the extremities of the body. Round 
about 
