jo (134) Society for Experimental Biology and Medicine. 



a half to two hours, most of the eggs die in the early stages of 

 development. 



It may also be mentioned in this connection that if eggs are fer- 

 tilized with sperm first and then exposed to the hypertonic sea 

 water of the above mentioned concentration for about two hours, 

 many more eggs will die without reaching the larval stage than 

 when the order is reversed. It is therefore obvious that the process 

 of membrane formation caused by the spermatozoon modifies the 

 sensitiveness of the egg to the hypertonic sea water in the same 

 sense as the> process of membrane formation caused by the acetic 

 acid. If eggs are fertilized with sperm and then exposed to the 

 hypertonic sea water for from about thirty to forty minutes, their de- 

 velopment becomes almost identical with that of the unfertilized 

 eggs treated first with acid and then exposed to the hypertonic sea 

 water for the same period of time. The majority of these eggs 

 segment and develop in a normal way. 



2. The question arises as to how far the division of labor be- 

 tween the two agencies used in these experiments goes. Does the 

 treatment with acid cause only the formation of the membrane, or 

 does it also set the internal mechanism of nuclear and cell division 

 into motion ? And what is the role of the treatment with hyper- 

 tonic sea water? From the author's earlier experiments he had 

 expected that the latter was required to cause the internal changes 

 necessary for karyokinesis. The direct observation, however, of 

 the eggs treated in the above-mentioned way with acetic acid, 

 shows that the acid treatment causes the formation not only of the 

 membrane, but also, in due time, of the karyokinetic spindle ; while 

 the eggs exposed for only thirty or forty minutes to the hypertonic 

 sea water do not show any karyokinetic changes nor, in fact, 

 changes of any kind. 



It is a striking fact that the spindle formation which can be 

 observed in the living egg of Strongyloccntrotits seems to be iden- 

 tical in the cases of the fertilized egg and the unfertilized egg 

 treated with acetic acid in the above-mentioned manner. The role 

 which the subsequent treatment with hypertonic sea water for from 

 thirty to forty minutes seems to play, is, in the first place, the accel- 

 eration of the process of segmentation. When the eggs are treated 

 first with acid and then for about thirty or forty minutes with 



