REPRODUCTION. 



539 



the antennae, the palps, and legs, under conditions which render it 

 possible that these nerves have the value of tactile nerves, and this is 

 the more probable since the sense of touch is principally discharged by 

 the antennae and the palps of the oral apparatus, as well as by the 

 tarsal joints of the legs. 



Olfactory organs are very generally distributed, as might have 

 been expected from the developed capability of tracking which many 

 insects possess. It may be regarded as fairly certain that the 

 surface of the antennae is the seat of the olfactory sense. Formerly, 

 in accordance with the views of Erichson, the numerous pits which 

 are found, for instance, on the leaf -shaped antennas of the Lamelli- 

 cornia, were interpreted as olfac- 

 tory pits ; but it is more correct to 

 regard with Leydig the peculiar 

 cones and knobs of the antennae 

 which are connected with gangliated 

 nerve endings as olfactory organs. 



The reproduction of insects is 

 principally sexual. The male and 

 female generative organs are always 

 placed in different individuals; but 

 they correspond in their position and 

 parts, and in their opening on the 

 ventral surface of the hind end of 

 the body. The testes and ovaries 

 are provided with paired ducts end- 

 ing in an unpaired portion (fig. 91). 

 The first rudiments of the genital 

 organs may be traced back to a 

 very early stage of the embryonic 

 development. Their development, 

 however, is only completed in the 

 latest period of larval life, or in insects with complete metamorphosis 

 during the pupal stage. In rare cases the full development and 

 maturity of the sexual organs is never completed, as in the so-called 

 sexless Hymenoptera (working bees, ants) and termites, which are 

 incapable of reproduction. 



The males and females are distinguished by more or less important 

 external differences in various parts of the body ; sometimes these 

 differences lead to a marked sexual dimorphism. The males are 

 almost always more slenderly formed, and are capable of quicker and 



FIG. 4i7. A portion of the nerve termina- 

 tion in the anterior leg of Locusta viri' 

 dlssima (after V. Graber). N, nerve; 

 Gz, ganglion cells; St, rods in the 

 terminal cells. 



