CLASS I: INSECTA. 



539 



at its base within 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 oro-ans 

 is situated at the extremity of the abdomen ; the female is fur- 

 nished with instruments of very various struct ui'c, 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 effects considerable leaps. In the 

 cockroaches, and some other insects, they form stout-jointed 

 bristles, resembling short antenna). 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 

 r. 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 oesophao-us 

 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 oi 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 

 a, head, antennae, &c. ; h, pharynx ; to the anal opening with but little deviation ; while in other 



c, crop; (f, gizzard; e, cbyle-forming ^.^ses it forms several convolutions in the anterior of the ab- 



stomach ; /, biliary vessels ; g, small , 

 intestine ; h, secreting organs ; i, anus, tiomen. 



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 diflferent 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.* 



DIGESTIVE APPARATUS OF AN INSECT. 



* With respect to the number of eggs laid by insects, it varies in diflferent 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 vulgaris, 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 latfter statement may appear, the fecundity of the queen bee is far inferior to that of 

 the white ant, Termes faUilis ; for the female of this insect extrudes from her enormous matrix innumerable eggs, at 

 the rate of sixty in a minute, which gives 3,<300 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 mtercourse is sufficient to impregnate, not only 

 the female parent, but all her progeny down to the ninth generation ! The original insect still continues to lay 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 5,904,900,000 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 



