256 PROBLEMS OF FERTILIZATION 



was initiated. In a careful analysis of his own results 

 Bataillon showed that for complete activation by 

 pricking it was necessary that blood or tissue extract 

 should be carried into the egg by the needle ; otherwise 

 the development was arrested without cleavage. Herlant 

 (1913, 1917) has confirmed this and has furnished a 

 simple cytological explanation of the result: Eggs that 

 are pressed from the body of the uninjured frog and 

 pricked with a clean needle complete maturation and 

 form a small first segmentation spindle so near the 

 center of the egg that its division produces no effect on 

 the cytoplasm of the egg, which remains undivided. 

 But if the eggs be moistened by blood before pricking, 

 asters arise in the cytoplasm at the point of pricking, 

 and by extension so affect the first segmentation spindle 

 that it remains relatively near the surface of the egg. 

 The division of this spindle then involves that of the 

 egg cytoplasm also, and development proceeds normally. 

 Tadpoles obtained by pricking have been reared to 

 maturity by Loeb and Bancroft. 



This method points to some very simple physical 

 change of the cortex as the primary event in activation. 

 Bataillon believed that the cortical change, which he 

 spoke of as a contraction of the egg, involved an excre- 

 tion of fluid containing substances such as CO 2 that 

 inhibited development. 



It is significant that recent studies in parthenoge- 

 netic activation (Loeb, R. S. Lillie, Bataillon) point to 

 changes in the cortical zone of the egg protoplasm as 

 the primary factor in activation. While the precise 

 nature of these changes still remains obscure, it seems 

 obvious that their effect is to release reactions within 



