THE PHYSIOLOGY OF FERTILIZATION 133 



in initiation of development. Such a substance might 

 conceivably be lost by the spermatozoon without detri- 

 ment to its vitality, leaving the spermatozoon in a 

 motile condition but without capacity for fertilization. 



The conception of a fertilizing substance borne by 

 the spermatozoon seems to be a necessary one, but the 

 conception that it acts on the egg as a cytolytic agent 

 is no longer maintained. The attempt has been made 

 by a number of investigators (Winkler, 1900; Gies, 

 1901; Robertson, 1912) to extract such a substance 

 from spermatozoa, but without success in the produc- 

 tion of a solution that will cause development of the 

 egg of the same species. 



T. B. Robertson (1912) has extracted, by a very com- 

 plex process, from the sperm of the sea urchin an acid- 

 soluble substance which caused the production of 

 atypical membranes on sea urchin eggs, especially 

 where the action was reinforced by previous treat- 

 ment of the eggs with f NSrCl 2 . No development 

 took place. It seems doubtful to the writer that this 

 represents the specific membrane-producing substance 

 of the spermatozoon, as Robertson maintains. The sub- 

 stance proved markedly poisonous to the eggs, an effect 

 that was not removed by treatment with hypertonic sea- 

 water. It seems possible that some cleavage product of 

 the sperm proteins was concerned. As the results of 

 other authors (Gies, etc.) have been negative, and, more- 

 over, as Loeb has treated the subject quite fully in his 

 book on Artificial Parthenogenesis and Fertilization (chap. 

 xix), we need not consider this matter in detail. 



A mere negative finding in this type of experiment 

 is, however, inconclusive. It is conceivable, as Loeb 



