PARTICULATE THEORY OF HEREDITY 241 



respects, viz., in that each one may change {mutate) with- 

 out the others changing, and in segregation and in crossing 

 over each pair is separable from the others. 



5. ''The Organism as a Whole/' or The Collective 

 Action of the Genes 



Several writers have stated their objections to the 

 particulate theory of heredity on the grounds of their 

 belief that the organism is a "whole.'' If this phrase is 

 intended to mean that there is some sort of an entity or 

 entelechy that directs all processes that go on in each 

 living thing, there is little to be said here, except that 

 this very old idea has not been found profitable as a 

 working hypothesis. It is improbable, however, that 

 many biologists mean to appeal to any such vitalistic 

 agency when they speak of the "organism as a whole," 

 but have rather some other idea in mind. I am inclined to 

 think that certain phenomena of embryonic development 

 are responsible for the slogan of the "organism as a 

 whole. ' ' In the segmentation of the egg the entire chromo- 

 somal complex is distributed to every cell in the body. 

 Each cell inherits the whole germ-plasm. How then it 

 may be asked can the result depend on the particular 

 make-up of its chromosomes rather than on the action of 

 the whole material? 



Granted that we know very little about the interactions 

 between the cells that cause some of them to differentiate 

 in one direction, others in other directions, yet if one fer- 

 tilized egg should begin its development with one kind of 

 material, and another egg with a different material, should 

 we not expect the end products to be different, irrespective 

 of the way in which the materials were present in the 

 original eggi No matter where the differences may lie, 

 i.e., whether in the nucleus or in the cytoplasm, there is 

 nothing here in any way inconsistent Avith this particulate 

 theory of the composition of the germ-plasm. On the 

 contrary, the only conclusion that seems at all reasonable 

 16 



