THE BIOLOGY OF THE CELL SURFACE 



Thus the term, Individuality of the chromosomes or of 

 their constituent genes, Is of restricted meaning. I can 

 not see how a given chromosome or a gene in the fertilized 

 egg should be the same individual in every cell of the body 

 of an adult male including every one of the billions and 

 billions of spermatozoa that such an animal, like the trout, 

 for example, sheds during its life-time. With regard to the 

 "individuality" of the genes or the chromosomes genetics 

 has offered us nothing except a term, which, as we have 

 seen. Is not even clear. From this point of view the gene 

 theory certainly can not give an explanation of the develop- 

 ment of an egg into an adult organism. 



Let me hasten to state that in company with the majority 

 of biologists I consider the weight of evidence sufficient 

 for the assumption that the chromosomes have to do with 

 heredity. As I have pointed out already, I see in the 

 nucleus that component of the cell which tends to maintain 

 the specificity of the cells by Its change-resisting character. 

 Then the chromosomes maintain Individuality or identity. 

 This maintenance however, as we have seen, can only come 

 through growth at the expense of the cytoplasm. This fact 

 allows us to see In a new light this maintenance : It is brought 

 about by growth, the up-take of material that carries or 

 assumes the characteristics of that which Is already present 

 in the chromosome. Further, this maintenance of Identity 

 must stand In some relation to the source that furnishes 

 the material, namely, the cytoplasm. 



Counter to this fact of the growth of the chromosomes 

 at the expense of the cytoplasm runs the postulate of 

 those geneticists who seek to explain differentiation 

 by the gene-theory of heredity, namely, that the genes 

 are factors which order the developmental processes 

 by giving up substance to the cytoplasm. But even 

 If the upholders of the gene-theory of heredity accept 

 the fact that the chromosomes grow at the expense of 



324 



