482 



CHARLES RUSSELL BARDEEN 



during gastnilation but are less marked except in the central 

 nervous system. In specimens exposed after the anlages of the 

 head and tail are formed, the heart and blood vessels are far less 

 affected than in earlier stages and blood corpuscles are found in 

 much greater numbers. The musculature and chorda are but 

 little affected. 



In a batch of frogs' eggs exposed in the neural groove stage for 

 fifty minutes all specimens showed marked abnormalities at the 

 time of hatching and none long survived this period. Data at 

 hand make it uncertain whether or not frogs' larvae at this period 

 are usually so much more susceptible than toad larvse as this 

 experiment would indicate. 



6. From the period of hatching to the period of 



metamorphosis 



Several experiments were made to test the affects of exposure 

 during this period but they were far fewer in number and less 

 varied than those made during the preceding stages. 



TABLE 7 

 Irradiation at stages between closure of blastopore and metamorphosis 



Experiment A 



