Centrosouie in Enucleated Egg-Fragments. 309 



My cutting experiments were performed at two periods, one 

 immediately after release and the other an hour and a half later. 

 From these we can by no means determine exactly when the 

 cytoplasm acquires the power of producing the centrioles and 

 ray system. What brings about the change in the characters of 

 the cytoplasm during this interval? In all probability the inter- 

 mingling of the nuclear fluid and cytoplasm during the time of 

 fading of the germinal vesicle gives to the cytoplasm the aster 

 producing power. A striking difference betw^een the matured 

 and immature cytoplasms has been described by many observers. 

 Delage emphasizes the fact that during this period, when the 

 cytoplasmic maturation takes place, the eggs become fecundable 

 both in Strongylocentrotus ('99) and in Asterias ('01.) Wilson 

 verifies this phenomenon in the eggs of Cerebratulus ('03, p. 417). 

 Spermatozoa can enter immature eggs freely, but they remain 

 undeveloped. (O. and R. Hertwig,'89, p. 199; Wilson, '96, p. 149.) 

 In immature cytoplasm not only is the development of the sperm 

 nucleus and ray system inhibited, but also the centrioles do 

 not arise in eggs, even if they are treated by salt solutions. 

 Morgan ('99) noticed that cytasters did not develop either in the 

 egg of Sphaerechinus or of Sipunculus before maturation begins, 

 and I was told by Professor Wilson that he observed the same 

 fact in the MgClj egg of Toxopneustes. Leaving open for the 

 present the question how the nuclear fluid acts upon the cytoplasm 

 w^e can at least say that the matured cytoplasm is ready to produce 

 or, in other words, has the power to form centrioles as well as 

 rays as a result of certain stimuli, this being in our case a CaCk 

 solution. 



As to the origin of the centrioles in the cytasters there are tw^o 

 possibilities besides the one just mentioned. First, as suggested 

 by Meves the centrioles might multiply in the cytoplasm during 

 the growth period of the egg and become the centers of the cytas- 

 ters under the action of a salt solution. Such an assumption is 

 not in contradiction with what has just been said, that asters do 

 not develop in unmatured cytoplasm even when the spermatozoon 

 brings a centriole into the egg, since the centrioles might be 

 present, but incapable of producing asters until the germinal 

 vesicle fades. There is another possibility similar to the above, 

 namely, that centrioles may be present as such in the nucleus and, 

 at the dissolution of the germinal vesicle, escape into the cytoplasm 



