EGGS OF ASTERINA (PATIRIA) MINIATA. 115 



used by Loeb have merely served to hasten a natural process and 

 to cause it to occur in a larger percentage of eggs. 



Something in addition to membrane formation occurs in the 

 eggs handled by Loeb, for they go ahead and segment as do 

 normally fertilized eggs, while the eggs that form spontaneous 

 membranes do not segment. From this it would appear that the 

 so-called "fertilisation membrane" is not an essential feature of 

 development, but merely its usual accompaniment. Thus the 

 voluminous literature dealing with artificial membrane formation, 

 as though it were the most important event in the initiation of 

 development, loses some of its force. Loeb himself recognized 

 that development, at least in Asterina, could proceed without 

 membrane formation ; witness his statement, corroborated by my 

 own observations, that spontaneous parthenogenesis proceeds 

 without the preliminary of membrane formation. He seems to 

 suggest, however, that this is not to be considered as typical de- 

 velopment, since it begins later, goes more slowly and results less 

 normally than in the case of fertilized eggs. Exactly similar 

 results may be obtained, however, in fertilized eggs by the use of 

 agents that retard development, such as cold, hybridization, 

 anaesthetics, etc. So we must admit that real development may 

 occur without membrane formation, and that membrane forma- 

 tion may occur without initiation of development. The two 

 processes are independent though they usually are associated 

 in normal ontogeny. 



The Development Spontaneously of Partheno genetic 

 Eggs of Asterina. 



According to Loeb, the development of the chemically fertil- 

 ized eggs differs from that of the spontaneously fertilized eggs 

 in two respects ; first, in forming membranes ; and second, in be- 

 ginning earlier and proceeding more rapidly. With this distinc- 

 tion I fully agree. Evidently, in the chemically fertilized eggs, 

 something in addition to membrane formation takes place, a 

 something that results in prompt initiation of the changes ex- 

 pressed by cleavage. In the spontaneously parthenogenetic eggs, 

 however, initiation to development is very slow in beginning, and 



