REPRODUCTION 99 



ducts, the 'micropyles' through which the spermatozoa make their 

 way to fertilize the egg. 



The eggs are carried down the oviducts by waves of peristalsis, 

 and deposited singly or in masses according to the habits of the 

 species. They are generally coated with the secretion of the accessory 

 glands which may serve to glue them to the surface or to bind them 

 together in a protective sheath. In the Hydrophilid water-beetles the 

 accessory glands produce silk from which an elaborate 'egg cocoon' 

 is formed; in the cockroach the eggs are cemented together by fluid 

 which hardens to form a tough 'ootheca'. In this insect the protein 

 secreted in the left colleterial gland is tanned and hardened by means 

 of the quinone formed by oxidation of protocatechuic acid secreted 

 in the right colleterial gland. 



Mating, impregnation and fertilization 



Many different kinds of stimuli are concerned in the mutual attrac- 

 tion of the sexes at mating, In many Diptera-Nematocera, Trichop- 

 tera, Plecoptera, &c, the females are attracted to the males by their 

 dancing in swarms; crickets and grasshoppers by their chirping 

 songs; and the males of Lampyrid beetles are attracted by the lumi- 

 nous organs of the female. But the most important stimuli are 

 probably scents. The females of many insects have glandular scent- 

 producing organs in the neighbourhood of the sexual opening. These 

 are particularly well developed in the females of such Lepidoptera as 

 Lasiocampidae and Bombycidae, in which the eggs of the female are 

 ripe for laying at the time of emergence from the pupa. The males of 

 these moths have enormously developed plumose antennae which 

 are specialized for the perception of the female scent. By following 

 this scent up-wind they can locate the female from a distance of 

 several miles, and are readily attracted to other objects contaminated 

 with the scent. In the silkmoth Bombyx, the gipsy moth Lymantria, 

 and the cockroach Periplaneta, the chemical structure of the sexual 

 scent has been worked out. In the honey-bee the 'queen substance' 

 secreted by the mandibular glands serves also as a sexual attractant 

 during the nuptial flight. In many Lepidoptera there are scent scales 

 or 'androconia' also in the male; the scent which they produce serves 

 to excite the female to accept the courting male. 



