450 CHARLES RUSSELL BARDEEN 



stamp of its own specific characters upon the early developmental 

 stages of the organism, while the egg cytoplasm furnishes only 

 the material for the formative operation of the combined nuclear 

 material of the two parents" (Newman). This conclusion is 

 strongly supported by the action of irradiated spermatozoa on 

 the eggs they fertilize. 



2. EFFECTS OF THE EXPOSURE OF MATURE OVA TO THE X-RAYS 



Owing to a rapid loss of capacity for fertilization by am- 

 phibian eggs after being laid in w^ater it is necessary to expose 

 the eggs within the body of the female. Here the eggs are to 

 some extent protected from the rays by the overlying tissues. 

 This perhaps accounts for their, relative insusceptibility to short 

 exposures or weak rays. On the other hand, thus exposed to 

 powerful rays for an hour or more the eggs are very susceptible. 

 In the following table the results of seven experiments are recorded. 

 Several other similar experiments were tried but proved unsuc- 

 cessful owing, usually, to lack of maturity of the eggs or to the 

 fact that all the ripe eggs had previously been discharged. Uter- 

 ine ova are prevented from maturing by irradiation. 



In each of the experiments recorded the body was opened after 

 the irradiation and a considerable number of eggs were fertilized 

 with an emulsion prepared from the testicles of one or more 

 normal males. In Experiment 1, table 2, twelve minutes exposure 

 had but slight effect. When so large a number of eggs are arti- 

 ficially fertlized and kept in glass dishes a similar percentage fre- 

 quently shows some defects in late larval and early tadpole stages, 

 owing to the overcrowding. In Experiment 2, thirty minutes 

 exposure gave decided results. The effects of exposure began to 

 be noticed in many specimens early in larval differentiation and 

 over 50 per cent of the eggs showed marked abnormalities before 

 the larvae reached the period of hatching. After forty-five 

 minutes exposure, Experiment 3, the results are still more marked 

 while after an exposure of an hour or more. Experiments 4-7, 

 many specimens showed abnormalities during gastrulation and 

 few developed into normal tadpoles. 



