212 KANSAS UNIVERSITY SCIENCE BULLETIN. 



ception of their action that we can entertain is that they bear 

 definite and progressively different relations to their cytoplas- 

 mic environment. Differentiation, we should therefore be in- 

 clined to say, is due to a series of adjustments between two 

 constantly varying and interdependent structures, nucleus and 

 cytosome, with the chromosomes acting as the measure of their 

 interaction. 



There has been in reality but one thing postulated as a basis 

 for my views regarding the organization of the chromosomes, 

 viz., that they are specific, self-perpetuating morphological 

 units. If this be granted, synapsis, segregation and double 

 chromosome groups necessarily are true conceptions, for there 

 is no other way of accounting for the reduction in the number 

 of chromosomes in mauration and the restoration of this num- 

 ber in fertilization. Once it is conceded that the chromosomes 

 are self -perpetuating cell units, then there can be no question- 

 ing the fact of a reducing or segregating division, for if a set of 

 chromosomes from the father enters the egg and duplicates a 

 set already present no other explanation of the reappearance 

 of the same two sets in the mature germ-cells can be offered. 

 The whole question of heredity based upon chromosome struc- 

 ture centers here. Every fact that makes for the establishment 

 of the chromosomes as definite structural elements is an argu- 

 mient in favor of a reducing or segregating division. The loss 

 of the identity of the chromosomes in any period of cell pro- 

 liferation means the recreation of the chromosomes in the next 

 mitosis. This fact must be clearly realized. If they are not 

 continuous structures they are new structures in each cell. If 

 they are neiv structures, then it must be explained how they 

 reappear in the same number, size and form from generation to 

 generation of cells and throughout the species, genus and 

 family of the grasshoppers. To say that they form anew after 

 each mitosis is to postulate an organization outside of them- 

 selves that controls their reintegration. This merely begs the 

 question, for we know of no such organization. I maintain that 

 the discovery of the same group of chromosomes in all the 

 species of Hesperotettix is alone sufficient to establish the fact 

 that they are self-perpetuating individuals. We actually see 

 them reproducing themselves in one mitosis after another, and 

 we find them invariably in every animal that we study. 



Now, in arguing thus for the continuity of the chromosomes, 

 it is not intended to convey the idea that they are always of 



