56 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



a single criterion which allows us to decide whether an agent 

 has an effect upon the egg similar to that of the entry of the 

 spermatozoon; this criterion is the development of the egg 

 into a larva. The mere initiation of cell division is not sufficient 

 since, for example, cell divisions occur in the cases of the growth 

 of tumors and galls, which do not lead to the formation of a 

 larva. This distinction between a cell division which forms the 

 basis of normal development and growth and one which leads 

 to the formation of pathological products is also of practical 

 importance. 



It is not our purpose in this book to report all the investi- 

 gations upon artificial parthenogenesis. We shall rather con- 

 fine ourselves to those experiments which help us to obtain an 

 insight into the physicochemical character of the process of 

 development. We will start with the experiments upon sea- 

 urchin eggs, which appear to be best suited to such investiga- 

 tions. The forms of sea-urchins with whose eggs I have worked 

 are Arbacia of the Atlantic Ocean (at Woods Hole) and Strongy- 

 locentrotus purpuratus and franciscanus of the Pacific Ocean (at 

 Pacific Grove). 



The eggs of both these forms develop only when incited 

 thereto either by sperm or by the chemical methods hereafter 

 to be described. 



