92 A. RICHARDS. 



on the division of animal cells," found in Ascaris eggs a retarda- 

 tion of the early cell divisions which was followed by death. 

 According to them, a short radiation causes an acceleration of 

 division. 



Fraulein Hertwig investigated the effect of radium on Ascaris 

 eggs to find evidence as to whether the chromatin and other 

 nuclear structures are directly affected by radiation, as claimed 

 by O. and G. Hertwig, or whether the rays act to break down 

 lecithin and affect the chromatin only indirectly, as held by 

 Schwarz, Schaper and others. Her evidence goes to support the 

 former view. Furthermore, she is not in agreement with all 

 previous work on this form. She finds cytological evidence that 

 even in the first division after exposure the chromatin is affected, 

 although Perthes speaks of what might be regarded as a latent 

 period. She agrees with Barlow and Bonney that exposure 

 causes a retardation, but was unable to secure acceleration of the 

 divisions even with so short an exposure as five minutes. The 

 amount of retardation depends to some extent on the length of 

 radiation, eggs radiated one hour with a given preparation de- 

 veloping farther than those radiated two hours. 



Negative results in exposing eggs of sea urchins to X-rays 

 have been reported by both Schwarz and Bardeen, but the 

 recent brilliant studies of Gunther Hertwig as well as the older 

 paper by Bohn on the effect of radium on these forms make it 

 desirable to repeat the experiments with X-rays. Hertwig's 

 results, like those of Fraulein Hertwig, were chiefly concerned 

 with the behavior of nuclei of exposed eggs and his results are 

 convincing along that line. During the course of his experiments 

 he noted that the progress of division in the sea urchin eggs, 

 which had been fertilized with sperm exposed to radium bromide 

 rays, was very greatly retarded even from the first cleavage. At 

 the end of the second day most of these eggs had died, after a 

 decidedly irregular course of development. His most important 

 results do not bear upon the question here under discussion. 



Bohn found that an exposure to radium of forty minutes 

 accelerated segmentation in eggs of the sea urchin, although a 

 longer exposure retarded it. 



The only previous experiments upon Gasteropods, so far as I 

 am aware, are those of Tur upon the development of eggs of the 



