Evidence from Metazoan Germ-Cells 29 



profound modification of it." ^"^ And still more recently 

 he has said, "Many biolo^^ists maintain that the nucleus and 

 more particularly the chromosomes are tlie exclusive seat (jf 

 the 'inheritance material' and that all the 'determiners' of 

 adult characters are located in them. Against the extninc 

 form of this theory many general and s])ecific objections 

 may be urged. General objections are based upon the con- 

 sideration that the entire cell, cytoplasm as well as nu- 

 cleus, is concerned in differentiation and that neitiier is 

 capable of embryonic development in the absence of the 

 other. Differentiation is indeed the result of the interaction 

 of nucleus and cytoplasm, and how then can it be said that 

 the nucleus is the only seat of the inheritance material.''" ^* 



An elaborate discussion of whether the language here used 

 can be harmonized with the statement (juoted above about 

 the demonstration of the correctness of the chromosome 

 theory, by saying that the views expressed in the last quota- 

 tion merely involve a "profound modification of the nuclear 

 inheritance theory" would smack too much of pure dialectics 

 to deserve a place in this volume. Our sole concern is with 

 the truth about the thing itself. 



Conklin's position would be so far satisfactory if he 

 would permit/us to understand his statements "the entire 

 cell, cytoplasm as well as nucleus, is concerned in differentia- 

 tion," and the one about modification of the nuclear inheri- 

 ance theory, to mean that cytoplasm is "inheritance mate- 

 rial" and contains "determiners." Evidence that cytoplasm 

 contains "determiners" is even more jjositive tlian is that 

 for the theory that chromosomes are the seat of such things, 

 for the simple reason that we can observe abundantly cyto- 

 plasm. in the act of producing hereditary structures, wiiereas 

 we rarely observe chromosomes operating directly in this 

 way. But such permission would not, I fear, be forthcoming. 

 If it would be, one is at a loss to understand why the terms 

 "hereditary substance," "physical basis of heredity," "de- 



