CLASS I. INSECTA. 
639 
at its base wltliin the one preceding it, so that the whole is Capable of bending to a certain dis- 
tance in some directions. The orifice of the generative organs 
is situated at the extremity of the abdomen ; the female is fur- 
nished "with instruments of very various structure, adapted for 
placing the eggs in the situation most proper for their develop- 
ment. The apex of the abdomen is also sometimes furnished 
with long filiform tails, sometimes with bristle-like organs, by 
means of which the insect eff'ects considerable leaps. In the 
cockroaches, and some other insects, they form stout-jointed 
bristles, resembling short antennae. In the earwigs they con- 
stitute a powerful pair of forceps, often of great length ; while 
the aphides are furnished with a pair of tubular appendages, 
from which a sweet juice exudes. 
The intestinal canal always forms a tube of variable width, 
formed of three membraneous layers, running from one extremity 
of the body to the other, commencing behind the mouth in a 
narrow oesophagus, and usually terminating posteriorly in a 
somewhat dilated cavity, the cloaca^ which also receives the ter- 
mination of the internal generative organs. The oesophagus 
leads first into a membraneous, and usually folded stomach, the 
crop ; from this, in the masticating insects, the food passes into 
a second stomach, which, from its being furnished with horny 
plates and other organs for the comminution of the food, has 
received the name of gizzard. Behind this is the true stomach, 
in which the process of chylification goes on. This is often 
covered with little villi, or furnished with glandular organs, 
which appear to secrete a gastric juice of some kind. The re- 
mainder of the canal forms the intestine, which is usually of a 
tubular form, and is very variable in length, sometimes running 
to the anal opening \vith but little deviation ; while in other 
cases it forms several convolutions in the anterior of the ab- 
domen. 
The nervous system of insects generally consists of a brain 
placed above the oesophagus, with ganglia variously distributed in the different species. The 
organs of sense are possessed in difi'erent degrees by different races. Insects are unisexual, with 
very few exceptions. Their reproduction is essentially oviparous, though some species are ovo- 
viviparous. The aphides are truly viviparous, at certain periods, the young being produced 
apparently by a sort of internal gemmation.* 
* "With respect to the number of eggs laid by insects, it varies in different species. The flea, for example, lays 
about twelve, and many diptera and coleoptera average, perhaps, fifty ; but others are far more prolific. Among 
moths, for example, the silk-worm produces five hundred, and some from one thousand to two thousand. The wasp, 
Vespa mdgaris, deposits three thousand ; the ant, Formica, from four thousand to six thousand ; and Kirby and 
Spence consider that, in one season, the number laid by the queen bee may amount to forty or fifty thousand, or 
more ; yet, surprising as this latter statement may appear, the fecundity of the queen bee is far inferior to that of 
the white ant, Termes fatalis ; for the female of this insect extrudes from her enormous matrix innumerable eggs, at 
the rate of sixty in a minute, which gives 3,600 in an hour, 86,400 in a day, 2,419,200 in a lunar month. How long 
the process of oviposition continues in the termite is unknown ; but if it were prolonged throughout the entire year, 
the amazing number of 211,449,600 eggs would proceed from one individual; setting, however, the number as low as 
possible, it will exceed that produced by any known animal in the creation. 
The Aphides, or plant-lice, furnish a remarkable instance of fecundity. In these insects, it has been satisfactorily 
ascertained by Bonnet, Lyonnet and Reaumur, that a single sexual intercourse is sufiicient to impregnate, not only 
the female parent, but all her progeny down to the ninth generation ! The original insect still continues to la}' when 
the ninth family of her descendants is capable of reproduction, and Reaumur estimated that, even at the fifth genera- 
tion, a single aphis might be the great-great-grandmother of 6,904,900,000 young ones. 
The impregnated ova of the aphis are deposited, at the close of summer, in the axils of the leaves, either of the plant 
infested by the species, or of some neighboring plant, and the ova, retaining their latent life through the winter, are 
DIGESTIVE APPARATUS OF AN INSECT. 
a, head, antennje, &c. ; b, pharynx ; 
c, crop ; d, gizzard ; e, chyle-forming 
stomach ; biliary vessels ; g, small 
intestine ; h, secreting organs ; i, anus. 
