EFFECT OF RADIUM ON FERTILIZATION 113 



Secondly, the sperm in many instances fails to gain entrance 

 into the egg. The engulfing of the sperm is undoubtedly due to 

 the activity of the egg, since the sperm is motionless from the 

 moment it becomes implanted in the egg membrane. Such ac- 

 tivities are incited by some substance in the sperm itself, and are 

 not due merely to the pricking of the membrane by the perfora- 

 torium, for in many instances the implanted sperm does not 

 enter. The seat of such a stimulating substance is not certainly 

 known. Probably it does not reside in the nucleus, since all of 

 activities of the egg, such as the throwing off of the cortical 

 layer, the formation of the fertilization cone, and its subsequent 

 movements, occur while the nucleus is still intact and entirely 

 outside of the egg. It is very likely that the stimulus resides 

 in the head cap of the, spermatozoon, and is injected into the egg 

 with the coagulating fluid. The failure of the sperm to enter is 

 due to the injury to this substance and a consequent failure 

 properly to activate the egg. Such an injury is not due specifi- 

 cally to the radium treatment since old spermatozoa, kept 

 fourteen hours in a vial will produce the same results. Probably 

 any treatment which weakens them in any way has this effect. 

 These two instances, I believe, indicate that the sperm proto- 

 plasm has been injured by the radium radiations. 



That the chromatin of the sperm has been injured has already 

 been pointed out. The difference in behavior between the 

 Nereis sperm and that of the sea urchin, as described by Hert- 

 wig, should be mentioned. In the former case, the sperm 

 nucleus fails to develop past a certain point, and fails to fuse 

 with the egg nucleus. The latter structure also fails to develop 

 due apparently to the failure of the sperm centrosome. In the 

 sea urchin, on the other hand, the sperm centrosome develops 

 perfectly, becoming the dynamic center of division for the egg 

 nucleus, which divides by itself as a rule in a normal manner. 

 If the sperm nucleus has migrated into a position close to the 

 spindle it acts as a foreign body in disturbing the normal be- 

 havior of the chromosomes. In some cases the two nuclei fuse, 

 but the sperm nucleus is soon eliminated in subsequent divi- 



