EFFECT OF RADIUM ON DEVELOPMENT OF CEL^ETOPTERUS. 5! 



bromide, previous to insemination, resulted in embryos which 

 were both normal and abnormal. In general there was little 

 difference between the results obtained from the short and from 

 the long exposures. Measurements of the nuclei in the radiated 

 embryos showed that they were approximately one half the 

 normal size and the development was presumably androgenetic. 

 The actual number of chromosomes could not be counted with 

 certainty. Hertwig states that "a certain answer to this ques- 

 tion (of the exact number of chromosomes) could be furnished 

 only by a study of the eggs during their early development. 

 Since this is impossible, owing to practical difficulties which the 

 material presents, the question must remain unsolved. " 



In the reverse experiment, in which frog sperm was radiated, 

 it was found by Gunther Hertwig ('n) that the same develop- 

 mental conditions obtained which he found when the egg was 

 radiated. Normal eggs fertilized by sperm which had been 

 radiated for short periods gave rise to abnormal embryos. But 

 if the sperm is radiated for a long period the embryos developed 

 normally. Later he repeated this experiment on the sea urchin 

 and found that although the intensely radiated spermatozoon 

 can penetrate the normal egg it fails to develop within the egg, 

 and brings about an abnormal type of cleavage. The egg nucleus 

 may divide by itself, sometimes normally, but more often ir- 

 regularly, as though the sperm had acted as a mechanical hin- 

 drance to orderly cleavage. When the sperm had not thus 

 interfered in the first mitosis it usually fused with the nucleus of 

 one of the blastomeres, thus causing abnormalities in the de- 

 scendants of that cell. In all of these cases the sperm aster 

 developed normally, the centrosome divided, and the daughter 

 centrosomes became the centers of the first cleavage figure. 

 This fact lead Hertwig to doubt Boveri's conception of the cen- 

 trosome as a permanent cell organ, and to incline to Lillie's view 

 that it is a result of the interaction of the sperm and the egg proto- 

 plasm. 



MATERIAL AND METHODS. 



The eggs of the tubicolous annelid, Chcetopterus pergamen- 

 taceus, are ideal for the type of experiments described in this 

 paper. They can be obtained fresh and in sufficient quantities, 



