FERTILIZATION-REACTION IN ECHINARACHNIUS PARMA. 30! 



Finally, the cytolysis theory assumes that the cytolysis of the 

 over-exposed egg is of the same nature as that of the egg which 

 has had through a lower exposure a membrane formed. This is 

 purely an arbitrary assumption. The over-exposed egg cyto- 

 lyzes rapidly because it is injured; the egg with the membrane 

 cytolyzes in spite of the membrane and at a slower rate. Accord- 

 ing to Herlant it is the failure to cleave that finally kills the mem- 

 brane egg. The cytolysis in these two classes of eggs thus springs 

 from different causes. Nor is this all. The thickening of the 

 cortex of the over-exposed egg we may regard as the initial step 

 in cytolysis or, if you please, as the mark of the injury that 

 hastens cytolysis. In the membrane egg, however, this cortex 

 has broken down through a process of liquefaction or secretion 

 which is the fundamental phenomenon in the cortical change of 

 which membrane elevation is a sequel. Therefore, the cytolysis 

 in these two kinds of eggs must differ not only in time but in the 

 quality of substances that cytolyze. 



For these capital reasons, then, added to the conclusion of the 

 results on Echinarachnius any theory of activation that postulates 

 the cause of the initiation of development as a superficial cytol- 

 ysis is difficult of defence. The cytolysis theory of development 

 has blocked the path of progress to an understanding of the fer- 

 tilization problem. 



B. The Rhythmical Changes of Cell Division. 

 Following successful insemination the egg divides. Cell divi- 

 sion is thus a criterion of fertilization. Many of the phenomena, 

 however, revealed by the egg subsequent to its insemination are 

 to be regarded as belonging not to the fertilization-reaction but 

 to the physiology of cell division. Among these we find rhyth- 

 mical changes that parallel cell division. For example, we may 

 cite those rhythmical changes in viscosity so carefully investi- 

 gated by Heilbrunn. He correlates these changes with the ap- 

 pearance and growth of the mitotic spindle during the division 

 cycle. Viscosity changes are, therefore, to be regarded as an 

 index to cell division. They are manifestations of the rhythm 

 of cell division and are in no wise peculiar to fertilization. Here 

 too belong other changes in the egg which follow insemination, 



