FURTHER EXPERIMENTS ON THE EFFECT OF HEAT 

 ON THE EGGS OF CUMINGIA. 



MARGARET MORRIS HOSKINS, 

 UNIVERSITY AND BELLEVUE HOSPITAL MEDICAL COLLEGE. 



I. Introduction. If the eggs of the mollusc Cumingia tellinoides 

 are heated during the prophase of the first maturation division, 

 the formation of the polar body is prevented. The nuclear divi- 

 sion continues, giving rise to two daughter nuclei, both of which 

 are retained in the egg. In the unfertilized egg these nuclei 

 fuse, so that the egg is in fact fertilized by the polar nucleus. 

 The course of the development which follows this self-fertilization 

 has already been described (Morris, '17). Since the publication 

 of that study, experiments similar to those producing artificial 

 parthenogenesis have been made on fertilized eggs. It was found 

 that if eggs are heated immediately after insemination they do 

 not form polar bodies, but proceed to the first cleavage at the 

 end of the warming. As these eggs should contain a triploid 

 instead of a diploid number of chromosomes, it was thought 

 that a study of them and a comparison with dispermic eggs might 

 yield interesting results. Theoretically, of course, the polar 

 nucleus is equivalent to a sperm nucleus, and either of these is 

 equivalent to the egg nucleus. The suppression of maturation 

 gives a chance for an interesting comparison between the sperm 

 and polar nuclei. Besides the experiments in which maturation 

 was suppressed, a control series of experiments was made to dis- 

 tinguish the effects of heating from those of the retention of the 

 polar nucleus. In this series, the fertilized eggs were heated 

 after they had completed the formation "of polar bodies. Any 

 abnormalities found in these eggs would obviously be the result 

 of the heat alone. 



A cytological study of eggs from the different sets of experi- 

 ments has been made and is presented in the following pages. 



II. Material and Methods. The technique of the experiments 

 is extremely simple and hardly varies at all from that used in 



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