242 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



and fertilization with sperm curtails the life of the larvae, and 

 prevents them from reaching the pluteus stage. For if we start 

 the eggs developing by the old osmotic method, i.e., with 

 gelatinous membrane formation, and then fertilize a cell of 

 the two- or four-cell stage with sperm while they are still ready 

 to segment, the next division of each of these blastomeres will 

 lead to the formation not of two cells, but of three or four. 

 To the astrospheres which are already formed in the cell by 

 the onset of parthenogenetic development, there are added 

 also the astrospheres formed through the influence of the 

 spermatozoon; thus the next division of the nucleus of such a 

 cell leads to the formation of more than two daughter nuclei, 

 which are also usually qualitatively unlike. They are there- 

 fore in the position of an egg fertilized by two spermatozoa, 

 and so have the same restricted vitality as is possessed by such 

 eggs. It is possible, however, that fragments which are ferti- 

 lized by sperm while they are in the process of partheno- 

 genetic cell division suffer more than normal eggs fertilized by 

 two spermatozoa. 



