48 



rilK CLASS OF INSECTS. 



of a whorl of long bristles. Those of L<-,<xt riridixxima (Fig. 

 slightly resemble toadstools. Fig. -"><>( represents the an- 

 terior pole of the egg with 

 the micropyles of Pyrrkocoris 

 a>h'riix. (From Gerstaecker.) 

 This contact of a male 

 sperm-cell with the yolk is 

 the fertilization of the egg. 

 From this moment begins the 

 life of the embryo. Fertiliza- 

 tion of the female germ by 

 means of the male sperm, 

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

 animals, but there are exceptions among insects. An embryo 

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

 this mode of generation has been applied by Leuckart the term 

 Parthenogenesis. Among certain species of insects there are 

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

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

 sisting of "asexual" individuals, which, as winter approaches, 

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

 of which lay eggs. This phenomenon, 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 Jelly-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, Trembly, Lyonet, Degeer, Kyber, and others, and 

 arrives at the following conclusions : 



"1. Ova deposited by impregnated female Aj>h itl<<* in autumn 

 are hatched in the spring. 



