VIII 



THE IMPROVED METHOD OF ARTIFICIAL PARTHENO- 

 GENESIS IN THE SEA-URCHIN EGG 



The first method of producing larvae from the unfertiUzed 

 egg of the sea-urchin by a mere increase of osmotic pressure f 

 only sufficed to show that the mysterious complex "living 

 spermatozoon" might be replaced by well-known physico- 

 chemical agencies. It did not lend itself well to a physico- 

 chemical analysis, since the method was not always reliable. 

 We have already mentioned that with the Cahfornian sea- 

 urchin S. purpuratus the method worked only with the eggs of 

 a small percentage of females and even the eggs of different 

 females of Arbada did not yield equally well to this method. 

 For a further investigation of the nature of the process of 

 fertilization this method was therefore very unsatisfactory. 



There were other reasons which indicated that a better 

 method for artificial parthenogenesis was needed. The larvae 

 of normally fertilized eggs rise to the surface of the water; they 

 are pelagic. The larvae produced by means of a hypertonic 

 solution rarely or never rose to the surface of the sea-water, 

 but swam g,t the bottom of the dish. And finally, the eggs 

 form, upon the entrance of a spermatozoon, the fertihzation 

 membrane. The unfertihzed eggs which developed after treat- \\ 

 ment with a hypertonic solution never formed a characteristic 

 fertilization membrane, but only a fine gelatinous film instead 

 of the clear fertilization membrane. 



This led me to think that the osmotic activation of the egg 

 was only an incomplete imitation of the fertilization process, 

 and that the fertilization by the spermatozoon perhaps depend- 

 ed not upon a single chemical agent, but upon a combination 

 of two or more which were only fortuitously combined in the 



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