51 1 471 ] 



lu treating of tlie development of insects it is necessary to refer to the 

 periodical casting of tjie larval skin. All tlie growth of insects takes 

 place in the larva state. Couseqnently no insect increases in size after 

 it has acquired wings. The larval skin seems to be an imperfectly or- 

 ganized membrane, which does not correspond in its growth to that of 

 the body, but yields to this growth, to a certain extent, by \irtue of its 

 elasticity. A time comes therefore when it can yield no farther. The 

 insect then evidently becomes oppressed, ceases to eat, usually retires 

 to some secluded spot, and, if gregarious, huddles together with its com- 

 panions, and there remains a day or two, almost motionless and with- 

 out food, and in an a])pareutly torpid and sickly condition. After a 

 time the distended skin bursts open, and the insect throws it off", and ap- 

 pears in a new, bright, and elastic skin, which, in its turn, is capable of 

 a certain degree of distension. This process, which is called moulting, 

 takes place three or four times in the course of the larval growth, and 

 in a few larvae which continue more than one year in this state, the moul- 

 ting is said to occur from five to eight times. In insects of very rapid de- 

 velopment, on the other hand, such as the maggots, or larva? of the 

 Muscidi©, no moulting takes place, and it is the larva; of this kind which 

 form coarctate pupae. 



THE SEXES OF INSECTS. 



As a general rule insects of different sexes resemble each other so 

 closely as to leave no doubt of their sijecific identity, and in many the 

 sexes can scarcely be distinguished. But this rule is subject to many 

 exceptions, and the naming of insects has been greatly confused by the 

 sexes of the same insect having been described and named as distinct 

 species. 



The sexual organs, especially those of the males, are usually conceal- 

 ed so as to be nearlj^ or quite invisible ; but the female, especially in 

 the order of Hymenoptera, often have an exserted o\ipositor of greater 

 or less length, which readily distinguishes them from the opposite sex. 

 An analogous structure exists in many wood-boring beetles which de- 

 posit their eggs in deep crevices in the bark of trees ; and more rarely 

 in insects of the other orders. In the Coleoptera the males are sometimes 

 distinguished by one or two horns, either upon the head or thorax, and 

 many of the predaceous beetles, both terrestrial and aquatic, have the 

 anterior feet much widened, and furnished beneath with a cushion of 

 hairs or bristles. 



The antennae usually differ in length but little, if at all, in the two 

 sexes ; but in the long-horned beetles (Cerambycidas) the antennae of the 

 males are generally considerably longer than those of the females. 



