95 



a passive role, and that any pre-deteiinination that may be present 

 is confined to the margin of the blastopore. If this be so, then we 

 may ascribe the destination of the cytoplasm of this part of the egg 

 to the " fate of position." * 



Even with regard to the polar mass of cytoplasm we have to 

 recall that the chief factor in its formation is the flowing of proto- 

 plasm to the animal pole. This is accompanied by the migration 

 of the nucleus, is particularly evident during the maturation phases 

 of the nucleus, and reaches its highest degree of intensity during 

 the entrance and fusion of the spermatozoon. Were our predecessors 

 wrong after all in ascribing the determination of the animal pole 

 and the position taken up by the centrospheres to the nucleus ? If 

 these are localised in the nucleus there is no need to look further 

 for evidences of localisation. 



In spite of the vast amount of work which has already been done 

 on this subject, the result of which has been to give a high degree 

 of importance to the cytoplasm, I am led by a consideration of the 

 meroblastic eggs of Teleostei to the conclusion that the orientation 

 of the egg is a function of the nucleus. 



* 1897, Meek, Post-Embryonal Development. — The Veterinarian. 



