ESSENTIAL FEATURES OF THE SEXUAL PROCESS 1263 



chemical in character. By alteration of the medium in which the eggs are 

 contained, Loeb has succeeded in imitating exactly the changes which 

 normally need the entrance of- a spermatozoon for their occurrence. On 

 immersing the eggs in a weak solution of formic or lactic acid, a membrane 

 is formed. The eggs are then taken from the acid, placed in concentrated 

 sea-water for a short time, and then removed to ordinary sea-water. Division 

 rapidly occurs with the production of a normal larva. He suggests that the 

 spermatozoon brings with it ferments or other chemical substances, which 

 excite the egg nucleus and cytoplasm in the same way as the chemical 

 measures adopted for this artificial induction of segmentation. 



