2O C. M. CHILD. 



in general the same. Materials which under the conditions exist- 

 ing during the developmental history of the egg cell accumulated 

 in the cytoplasm now become available as nutrition. During 

 its developmental stages the egg cell was in the presence of 

 abundant nutritive material brought to it by the activity of the 

 parent organism and its chief activity consisted in accumulation 

 of substance until the obstacles to metabolism resulting from 

 this accumulation or from increasing impermeability of mem- 

 branes made further metabolism impossible. At the time of 

 fertilization external nutritive material is not present or is present 

 only in minimal quantities, consequently, and in accordance 

 with chemical laws, the activity of the egg, as soon as increased 

 permeability or cytolysis has made such activity possible, con- 

 sists largely in the breaking up of the previously accumulated 

 material. It is not necessary to assume that any mysterious 

 transformation in the nature of the egg has occurred : its activity 

 merely changes with the presence or absence of external nutritive 

 material. The case is not very different from that of the plana- 

 rian which, in the presence of sufficient food, increases in size 

 and accumulates material and grows old, but when starved uses 

 up the previously accumulated material, decreases in size and 

 becomes young, at least morphologically (Child, 'lib). The 

 entrance into the egg in fertilization of another nucleus, the 

 sperm nucleus, which is in a condition somewhat similar to that 

 of extreme starvation undoubtedly accelerates the process of 

 dedifferentiation and rejuvenescence in the egg, but it does not 

 necessarily have any other effect so far as the initiation of develop- 

 ment is concerned. 



Fertilization then saves both the egg and the sperm nucleus 

 from death and initiates the process of dedifferentiation and 

 rejuvenescence by making further metabolism possible, either in 

 consequence of increased permeability or partial cytolysis. The 

 evidence seems to me to point toward the conclusion that the 

 primary influence of the sperm is an increase in permeability 

 rather than a cytolytic action, but whichever alternative is the 

 correct one the significance of fertilization remains the same. 



As dedifferentiation proceeds and the obstacles to metabolism 

 decrease in the egg, metabolism becomes more and more rapid. 



