THE EFFECT OF RADIUM RADIATIONS ON THE 

 DEVELOPMENT OF CH^TOPTERUS. 



CHARLES PACKARD. 



INTRODUCTION. 



The experiments described in this paper show that the egg of 

 Chcetopterus, if radiated for an appropriate length of time before 

 insemination will be injured to such an extent that its nucleus 

 plays no part in development. Nevertheless the sperm nucleus 

 divides normally; development is therefore androgenetic. The 

 history of the egg nucleus from the time of insemination until 

 it is absorbed into the protoplasm can be followed in detail. 



Similar experiments have been performed by Gunther Hertwig 

 ('u) on the frog's egg. He observed that if the eggs, after a brief 

 radiation, were inseminated with fresh frog sperm, the amount 

 of injury appearing in the embryos is proportional to the length 

 of exposure. But if the eggs are radiated for more prolonged 

 periods, cleavage becomes fairly normal, and the embryos, some- 

 what retarded in their rate of development, grow into swimming 

 larvae. These larvae are normal in shape but are smaller than the 

 controls and not as active, in these respects resembling partheno- 

 genetic larvae. He also observed that the nuclei of the cells in the 

 embryos developing from eggs radiated for considerable periods 

 are about one half of the size of the nuclei found in the controls. 

 Since the size of the nucleus, according to Boveri, varies with the 

 number of chromosomes contained in it, the inference is that 

 these embryos have developed under the influence of the sperm 

 nucleus and are therefore androgenetic. The egg nucleus has 

 been entirely prevented from taking part in development. 

 Cytological proof of this critical point was lacking. 



The experiments of Paula Hertwig ('16) on the eggs of Triton 

 do not wholly confirm the results just described. Exposures of 

 the eggs for 5 to 30 minutes to a preparation of 51 mg. of radium 



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