EMBRYONIC DEVELOPMENT 



393 



the experiments of the Hertwigs on frog eggs, and in addition to radium 

 these investigators have used X-rays and ultra-violet radiation. They 

 report that when ultra-violet is employed the effects which the Hertwigs 

 obtained occur more frequently than when either radium or X-rays are 



used. 



Packard (71, 73) has followed in considerable detail in Nereis and in 

 Chaetopterus the alterations in fertilization which occur after radiation. 

 In the case of Nereis Packard found that when normal eggs were fertilized 



50 40 50 60 70 



Duration of Exposure in Minutes 



Fig. 1. — Percentages of haploid and diploid cleavages in Chaetopterus eggs, which were 

 exposed to radium bromide and then fertilized by normal spermatozoa. The ordinate 

 represents the percentage of eggs which cleaved, and the abscissa represents the duration 

 of exposure in minutes. (From Packard, 73.) 



by radiated spermatozoa, the extent to which the eggs were stimulated 

 to development varied. In some cases the spermatozoon activated the 

 egg normally and was drawn into the egg cytoplasm, but normal cleavage 

 asters failed to develop and there was no fusion of male and female nuclear 

 material. In other cases, however, the radiated spermatozoon activated 

 the egg only to the extent of the extrusion of jelly and the formation of a 

 fertilization cone, but the spermatozoon was not drawn into the egg. 

 In Nereis, when the male and female nuclei do not fuse, the egg fails to 

 develop. In this respect the situation is different from that in Ascaris. 

 When Nereis ova were radiated, the maturation phenomena became 

 irregular and the ova failed to develop properly, even though they were 

 fertilized by normal spermatozoa. Packard found, also, that radiation 

 of fertilized eggs resulted in more extensive developmental abnormalities 

 than radiation of unfertilized ova. 



In the case of Chaetopterus Packard was able to obtain decisive quanti- 

 tative data with regard to nuclear behavior in radiated eggs which were 

 fertilized by normal sperm. These data are shown graphically in Fig. 1, 

 in which the ordinate represents the percentage of radiated eggs which 



