174 CARL RICHARD MOORE. 



tozoon it is complete, and bars further activation; but in acti- 

 vation by artificial agents we arbitrarily select the given condi- 

 tions, and if these are not the optimum conditions complete acti- 

 vation is not obtained. This is evidenced by the further reaction 

 with the sperm, that usually results in very abnormal develop- 

 ment. The main question at issue is: Can fertilization be supei- 

 posed on parthenogenesis? 



In the natural history of an egg there appears first a period 

 at which fertilization is not possible, even though sperm enter 

 the eggs. We say such eggs are not mature. Usually also at 

 this period artificial initiation of development is impossible. 

 Conditions are not such as will permit of even a start in the 

 developmental processes. This non-fertilizable condition is 

 followed by changes (maturation) that lead to a condition in 

 which fertilization is the normal behavior. In some eggs this 

 condition is retained but a short while and in others for a longer 

 period. In both cases however the eggs become immune to the 

 effect of sperm shortly after fertilization occurs; they have 

 returned to a non-fertilizable condition. 



Lillie has determined that at the time the capacity of fertiliza- 

 tion is gained the substance fertilizin is present in very large 

 quantities and that so long as this substance is being liberated, 

 fertilization normally follows the entrance of sperm. When once 

 this process has occurred, further fertilization is absolutely im- 

 possible; also fertilizin is no longer being produced by the egg. 

 If this substance is completely washed out of normal, ripe eggs 

 they can not be fertilized. 1 



The studies of E. E. Just ('15) very clearly reveal the loss of 

 some substance that escapes from the egg of Platynereis or is 

 changed into an inactive form by an extremely short exposure 

 to sea water. After such an exposure of the eggs, spermatozoa 

 may enter and call forth very slight changes more or less charac- 

 teristic of normal development, but are yet entirely unable to 

 lead on to cleavage stages and later development. The eggs 

 have returned to a non-fertilizable condition obviously due to 

 the absence of some substance which must be present if the 

 fertilization reaction is to be carried out completely. 



1 Lillie, '14, 



