EFFECTS OF KAYS OF RADIUM ON PROTOPLASM 



331 



Text fig. B. "Sea-urchin eggs radiated for forty minutes after insemina- 



tion. 



between cleavages is evidently increased in length in later 

 development since after several hours the embryos were far 

 behind the controls. These embryos are not abnormal except 

 in the fact that they are behind the controls. The retarding 

 effect of the beta rays, even after so short an exposure as 40 

 minutes is therefore permanent, even when the embryos are 

 placed in the best possible environment. 



Unfertilized eggs respond in the same way except that a longer 

 exposure is necessary in order to obtain the same results. 



When unfertilized eggs are treated with the slow and rapid 

 beta ,rays for 30 minutes or more and then inseminated with 

 fresh sperm they throw off a very slight fertilization membrane. 

 Cleavage is much delayed and a'most always irregular. The 

 few embryos which survive for a day show many abnormalities. 

 Most of them never pass through the gastrula stage, and those 

 that do, later show abnormalities of the types familiar to all who 

 have observed the development of Arbacia. A careful de- 



