48 THE CLASS OF INSECTS. 



of a whorl of long bristles. Those of Locusta viridissima (Fig. 

 .")(■) ^) slight]}' resemble toadstools. Fig. 56 c represents the an- 

 terior pole of the egg witli 

 the micropyles of Fyrraocoris 

 apterus. — {From Gerstaecker.) 

 This contact of a male 

 sperm-cell with the yolk is 

 the fertibzation of the egg. 

 From this moment begins the 

 life of the eml)rvo. Fertibza- 

 tion of the female germ l)y 

 means of the male s p e r m , 

 through tlie congress of the sexes, is the rule with bisexual 

 animals, but there are exceptions among insects. An embryo 

 may start into being without tlie interposition of the male ; to 

 this mode of generation lias been applied by Lenckart the term 

 Parthenogenesis. Among certain s[)ecies of insects there are 

 some individuals which, by a sort of budding process, and with- 

 out the aid of the male element, throw off sunnner broods, con- 

 sisting of "asexual" individuals, which, as winter ai)proaches, 

 are succeeded by a brood of true males and females, the latter 

 of which lay eggs. This phenonrenon, called by Steenstrup 

 "alternation of generations," has been observed among a com- 

 paratively few species, and the apparent design of such an 

 anomalous mode of reproduction is to afford an immense num- 

 ber of individuals, thus providing for the continuance of the 

 species. The individuals in whom this budding process takes 

 place are called "asexual" because, though they may resemble 

 the female sex outwardly, their sexual organs are only partially 

 developed. This budding process is the same in kind with that 

 observable in the Jellj^-fish, which throw off by parthenogen- 

 esis, or alternations of generations, summer broods of immense 

 extent, but in winter propagate by true eggs. Huxley has 

 studied the development of Aphis by parthenogenesis, the 

 anomalous nature of which had previously been discovered by 

 Bonnet, Tremljly, Lyonet, Degeer, K3'ber, and others, and 

 arrives at the following conclusions : 



"1. Ova deposited by impregnated female Aphides in autumn 

 are hatched in the spring. 



