M1CRODISSECTION STUDIES. 339 



of the egg, the blastomeres are practically non-adhesive, and they 

 maintain more or less spherical shapes till well on into the later 

 segmentation stages. 



6. THE LOCALIZATION OF A MATERIAL WHICH AFFECTS THE 

 LlFE OF THE L^NFERTILIZED STARFISH EGG. 



It is well known that immature starfish eggs can be kept in sea 

 water at room temperature for 36 hours or more without disinte- 

 grating. That the germinal vesicle or nucleus is responsible for this 

 length of life can be demonstrated by cutting an immature egg in 

 two. The nucleated fragment lasts fully as long as the entire egg. 

 The non-nucleated portion, on the other hand, disintegrates within 

 three to four hours. In mature unfertilized eggs the conditions 

 are quite different. In the mature egg the germinal vesicle has 

 broken down and the nuclear sap has diffused throughout the egg. 

 Loeb ('02) and Mathews ('07) showed that such eggs have a 

 higher rate of oxidation than immature eggs and if left unfer- 

 tilized, disintegrate within 8 to 10 hours whereas the immature 

 eggs last for days. 



The non-nucleated fragment of the mature egg lasts as long as 

 the whole egg, evidently owing to the dispersed nuclear sap of the 

 dissolved germinal vesicle. \Yhat is significant is that the nucleated 

 fragment lives no longer than the non-nucleated fragment. Both 

 contain the dispersed nuclear sap, while the nucleated fragment 

 possesses also the definitive mature egg nucleus which is ultimately 

 to become the female pronucleus. Apparently it is the dispersed 

 nuclear sap and not the definitive mature egg nucleus which is 

 chiefly concerned. In the formation of the nucleus of the mature 

 egg we have possibly something analogous to the state of affairs in 

 many Protozoa where the nuclear apparatus consists of a tropho- 

 or macro-nucleus concerned chiefly in the metabolic activities of the 

 cell, and the kineto- or micro-nucleus which has only to do with the 

 reproductive activities. In the starfish egg we may consider the 

 germinal vesicle as a combined tropho- and kineto-nucleus. On the 

 approach of maturation the tropho-nuclear material (nuclear sap) 

 diffuses throughout the egg, leaving behind the kineto-nuclear part, 

 the mature egg nucleus, which gives off the polar bodies to become 

 ultimately the female pronucleus. 



