94 A. RICHARDS. 



Comparable results were obtained by these same investigators 

 working on the eggs of Amblystoma. Exposures of fifteen 

 minutes daily first produced a period of acceleration which lasted 

 up to ten clays in some embryos, but at the end of four days ab- 

 normalities began to manifest themselves. Up to the tenth or 

 eleventh day the exposed eggs were larger than the controls; 

 after that they grew no larger, some became actually smaller, and 

 all were grotesque. The controls on the other hand continually 

 grew larger. 



In other eggs which were exposed daily four or five times, but 

 otherwise permitted to develop undisturbed, the tendency to 

 recover and develop normally was noted. This was not a clear 

 result, however, for in less than half of the eggs so exposed was 

 restitution of form affected, and all died after the exposure of the 

 twenty-third day. 



The occurrence of a latent period is reported by Schaper as one 

 of the results of exposing eggs of Rana fusca and of Triton to 

 radium. During the first day of his experiments no departure 

 from the normal course of development was noticed. Following 

 this "latent period," Schaper observed that the development of 

 the embryos was greatly interfered with, marked abnormalities 

 and finally death being produced. The duration of the latent 

 period depends upon the intensity of the radiation and upon the 

 state of development of the embryo at the time of exposure. 

 In nearly all cases it lasted a day, and if older larvae were used, 

 with relatively short radiation, it might last several days. The 

 course of development was always more or less drawn out, passing 

 into a condition of standstill to be followed at last by death. 

 In general, Schaper found that there were inhibitive effects on 

 cell division, embryonic differentiation, and embryonic growth. 



Bardeen has found by exposing either sperm, or eggs before 

 fertilization, or fertilized eggs to radium that abnormalities are 

 produced and he proceeds upon the hypothesis that the nuclei 

 are affected, thus causing the retardation in growth. "Cleavage 

 in most eggs fertilized by exposed sperms seemed to be normal. 

 In several of the experiments it appeared to be slightly more 

 rapid than in the control eggs." In mature eggs which were 

 exposed to X-rays and then fertilized with normal sperm "the 

 early cleavage stage appeared to be normal." 



