22 The Unity of the Organism 



upon which we have already drawn we read : "26. The 

 organization of the ovocyte is not the initial organization. 

 The yellow protoplasm (mesoplasm) of the Cynthia egg is 

 probably derived, at least in part, from sphere material 

 (archoplasm) which arose from the nucleus at the last 

 ovogenic division. The yolk (endoplasm) is formed by the 

 activity of the 'yolk matrix' (Crampton) which also is 

 probably sphere material. The clear protoplasm (ecto- 

 plasm) is derived from the germinal vesicle at the first 

 maturation division. Thus many important regions of the 

 egg come, at least in part, from the nucleus, and a method 

 is thereby suggested of harmonizing the facts of cytoplasmic 

 localization with the nuclear inheritance theory." 



Again, we find : "This truly remarkable condition in which 

 considerable portions of the cytoplasm are traceable to the 

 nucleus is of the utmost theoretical importance. From all 

 sides the evidence has been accumulating that the chromo- 

 somes are the seat of the inheritance material, until now this 

 theory practically amounts to a demonstration. On the 

 other hand, all students of the early history of the egg have 

 observed that the earliest visible differentiations occur in 

 the cytoplasm, and that the position, size and quality of 

 the cleavage cells and of various organ bases are controlled 

 by the cytoplasm. However, in the escape of large quanti- 

 ties of nuclear material into the cell body, and the forma- 

 tion there of specific protoplasmic substances we have a 

 possible mechanism for the nuclear control of the cytoplasm, 

 and when, as m the case of the ascidians and fresh water 

 gastropods, these substances are definitely localized in the 

 egg, and can be traced throughout the development until 

 they enter into the formation of tlie particular portions of 

 the embryo, a specific mechanism for the nuclear control of 

 development is at hand, and the manner of harmonizing the 

 facts of cytoplasmic organization with the nuclear inher- 

 itance theory is clearly indicated." 



