252 PROBLEMS OF FERTILIZATION 



vice versa, which he proposes to call the theory of 

 colloidal morphogenesis. There is no doubt, as we have 

 previously seen (p. 153), that such changes are involved 

 in cell division and hence in the phenomena of activa- 

 tion that initiate the first division of the egg. But it 

 seems to the writer that in the series of events of activa- 

 tion these changes do not come first that they are 

 effects rather than causes of activation. Delage is so 

 conscientious a critic of his own theory, which he says 

 attributes an undemonstrated role to intrinsic forces 

 of the egg, viz., of determining other phenomena than 

 those directly dependent on the action of the reagents, 

 that any other critic must be disarmed. The concep- 

 tion is, however, of great historical interest at least, 

 and it led Delage to discover one of the best methods 

 yet devised for activation of sea urchin eggs. A short 

 account of it is therefore desirable. 



Delage regards the "first event" (membrane forma- 

 tion), which precedes the segmentation of the egg, as 

 a coagulation; "the second event" (disappearance of 

 the nuclear membrane) as a liquefaction. He thus 

 came to the conclusion that if a coagulative effect could 

 be produced in the unfertilized egg by one reagent, 

 and if this were followed by a liquefactive effect pro- 

 duced by another reagent, development of the egg 

 might be induced. Regarding acids in general as coagu- 

 lating agents and alkalies as liquefying agents, he was 

 led to try the effect of successive action of acids and 

 alkalies on unfertilized eggs of the sea urchin. The 

 application of this method to eggs in sea-water was 

 without success, but it yielded very beautiful results- 

 in hypertonic sea-water. Tannin was finally selected 



