THE MORPHOLOGY OF FERTILIZATION 83 



ceives that the chromosomes of each germ nucleus are 

 qualitatively differentiated, and that a full representa- 

 tion of chromosome qualities is necessary for normal 

 development. His experiments constitute an argument 

 for qualitative differences of chromosomes which has 

 been generally accepted. The result is reached by ex- 

 exclusion of other possible causes of abnormality. 

 This subject leads into certain phases of cytology that 

 do not belong in our field. 



The case of the frog is somewhat different, in that 

 the nuclei are either definitely diploid or haploid. 

 Herlant comes to the conclusion that the cause of death 

 in this case is the different size of the nuclei and their 

 associated cell bodies in the same embryo, which renders 

 normal functioning impossible, and other more obscure 

 probable causes of disharmony associated with this 

 principle. 



For the subject of morphology of fertilization the 

 study of polyspermy is significant in two principal 

 respects: (i) It furnishes the demonstration that the 

 sperm nucleus is different from the egg nucleus, owing 

 either to association of a centrosome with it or for other 

 cause; because we find that each sperm nucleus pro- 

 duces a definite effect on the cytoplasm of the egg, the 

 formation of an aster, which the egg nucleus itself 

 does not produce in the cases studied. (2) The in- 

 evitable pathological result, when more than one sperm 

 nucleus is concerned in the development, furnishes 

 important evidence for the nuclear theory of heredity. 

 On the physiological side the study of polyspermy is 

 significant from other aspects, which we shall examine 

 later. 



