SUSCEPTIBILITY OF EGGS OF AMPHITRITE. 4! 



may be started into activity at definite intervals by mechanical agi- 

 tation. These processes are, for the most part at least, indepen- 

 dent of the processes that cause segmentation. I have noticed, 

 as a rule, that the riper the eggs are the more cleavage is found, 

 but I am convinced that it is never normal beyond the first few 

 segmentations, if at all. It would seem, then, that the sperm 

 introduces the active cause of this process. 



It has been shown by Lyon L in the fertilized Arbacia egg, that 

 there are recurring periods of susceptibility to KNC poisoning, 

 and to lack of oxygen. Each period of susceptibility is followed 

 by a period of resistance. On the other hand, in the unfertilized 

 eggs of Amphitrite, there are at certain times unstable conditions, 

 during which a small amount of agitation will set these unstable 

 forces free, and lead to some definite characteristics of more ad- 

 vanced development (/. e., production of cilia, etc.). 

 HULL ZOOLOGICAL LABORATORY, 

 UNIVERSITY OF CHICAGO. 



, E. P., Am. Jour. ofP/iys., 1902, Vol. VII., No. I. 



