ORIGIN OF THE INDIVIDUAL 249 



2. Metazoa 



Turning from Paramecium and its allies, we may consider 

 some evidence among higher forms in regard to the 'dynamic' 

 influence of fertilization. Although fertilization is usually 

 necessary for the resumption of the series of cell divisions 

 which paused after the maturation divisions, and which are 

 to transform egg into adult, there are many exceptional but 

 entirely normal cases where the egg proceeds to divide of 

 its own accord. Such parthenogenetic eggs are formed like 

 other eggs, though sometimes without synapsis and there- 

 fore without chromosome reduction. Thus the eggs of the 

 Honey Bee, to cite the most interesting case, develop either 

 with or without fertilization fertilized eggs forming fe- 

 males and unfertilized eggs, males. Certain species of Roti- 

 fers and Round Worms apparently reproduce solely by 

 parthenogenesis, males not being known. Leaving out of the 

 question the effect on the chromosome complex, it is at once 

 apparent that the mere fact that an egg divides without the 

 influence of a sperm indicates clearly that, in such cases at 

 least, neither structural additions nor physiological influences 

 of the sperm are necessary to initiate development. 



It may with justice be urged, however, that such cases of 

 normal parthenogenesis are special adaptations to peculiar 

 conditions in which the egg has usurped, as it were, the usual 

 sperm function, and that therefore the evidence is of little 

 weight in determining the primary significance of fertiliza- 

 tion. Accordingly the data from so-called ARTIFICIAL 

 PARTHENOGENESIS are particularly cogent. Within recent 

 years it has been found that the eggs of a considerable num- 

 ber of Invertebrates and even of Vertebrates, such as some 

 Fishes and Frogs, which normally require fertilization, can 

 be induced to start development 'parthenogenetically' by 



