156 NOTE ON ALTERNATION OF GENERATIONS 



birth to a butterfly ; and this butterfly must separate 

 itself into a crowd of butterflies before giving birth 

 to a lily." l Trembley's discoveries were followed by 

 the scarcely less astounding revelations of Bonnet as 

 to the production of Aphides, or plant-lice. The 

 aphis, a winged insect, deposits its eggs on the axils 

 of the leaves of plants in the end of summer ; these 

 eggs are hatched in the following spring ; the produc- 

 tion is a wingless, sexless insect. This wingless insect, 

 while a virgin mother, produces its young alive with 

 marvellous rapidity, in repeated births, during the 

 course of a few days. Within twenty-one days, one 

 single aphis has been found to produce ninety-five 

 young ones. These wingless aphides (virgins), so 

 produced, give origin to broods of similar wingless 

 aphides, the reproduction going on to the tenth or 

 eleventh generation, until, in the course of a single 

 season, according to Professor Carpenter, no fewer 

 than ten thousand million millions are evolved. In 

 the end, some of these lamal aphides are fully deve- 

 loped into males and females, through whose agency 

 ova are again produced, and the same cycle of deve- 

 lopment is repeated the following year. Professor 

 Carpenter regards the multiplication by the larvae as 

 a process of gei*mination, analogous to the multiplica- 

 tion of cells by sub-division ; while he holds that the 

 true generative process, analogous to the conjugation 

 of cells, is only performed when perfect aphides of 

 distinct sexes are evolved. 2 



The tabular view which Professor Owen gives of 



1 Lewes's Sea-Side Studies, p. 281. 



2 Carpenter on the Microscope, pp. 681, 682. 



