EFFECT OF RADIUM ON DEVELOPMENT OF CH.ETOPTERUS. 6 1 



abnormal nuclei in the later embryos, as he demonstrated cyto- 

 logically. The longer exposures so injured the egg nucleus that 

 it failed altogether to fuse with the sperm nucleus, and therefore 

 played no part in later development. The embryos were there- 

 fore androgenetic. 



He has brought forward no actual proof that this is the case in 

 the frog egg, except the evidence furnished by measurements of 

 the nuclei. Paula Hertwig has shown that when Triton eggs are 

 similarly treated the number of chromosomes is less than the 

 diploid number and probably the haploid number but of this she 

 is not certain. But Hertwig's explanation is in part supported 

 by the facts brought forward in this paper. A strict comparison 

 cannot be made since his conclusions were based on the length of 

 life of the embryos while mine have to do with the behavior of the 

 germ nuclei up to the time of the first cleavage. But in all 

 probability the same phenomena occur in both cases. 



The results obtained in the reverse experiment, in which the 

 frog sperm is first radiated and then added to fresh eggs, are of 

 the same order as the foregoing. Up to a critical time the radi- 

 ated sperm produces greater and greater abnormalities in the 

 embryo; after that period, more intensely radiated sperm pro- 

 duces more normal embryos. The original experiment of O. 

 Hertwig ('n) has been repeated by G. Hertwig ('12), Opperman 

 ('13) and others with the same results. A cytological study of 

 the eggs of the sea-urchin fertilized by radiated sperm has been 

 made by G. Hertwig ('12). He found that after prolonged 

 radiation the sperm retained their motility and entered the egg, 

 but the sperm nucleus never increased to its normal size in the 

 egg. As a rule it lay as a foreign body outside of the dividing 

 egg nucleus, but occasionally it became involved in the spindle 

 and the division was rendered abnormal, probably because of the 

 mechanical interference. In such instances the sperm nucleus 

 was carried passively into one of the blastomeres later fusing 

 with the nucleus of that cell. The subsequent development of the 

 cell and its descendants was abnormal. On the other hand, a 

 shorter radiation injured the sperm nucleus but it fused with the 

 egg nucleus. Later it was thrown out as in Chcetopterus. In 

 such instances the egg nucleus divided abnoimally and cleavage 



