MULTIPLE CHROMOSOMES 573 



If the chromosomes are homogeneous and identical, as Delia 

 Valle asserts, their substance could most easily be di\dded while 

 they were in 'solution.' The complication of the mitotic proc- 

 ess is all out of proportion to the simple end to be served under 

 such an assumption. 



6. Chro7nosome distribution 



In most mitoses it would seem that every step of the process is 

 directed toward seciu-ing the exact distribution of the chromatin 

 elements. The outstanding exception to this rule has been the 

 independent movement of the accessory chromosome in one of 

 the maturation mitoses, where it goes into one cell entire without 

 division. This is clearly a differential mitosis, featured by an 

 asymmetrical distribution of the chromosomes. One of the 

 elements possesses a distinctive character not shared by the 

 others — it has an individual and more or less independent move- 

 ment which takes place at only one time in all the history of the 

 organism. Up to this one point it is distributed in mitosis like 

 the other chromosomes, but just here it betrays the inherent 

 difference of its nature. So much of the chromatin substance 

 acting as a unit in mitosis, possesses distinctive characters. Are 

 these the consequence of this separate unity, or is there some 

 specific nature of the material? The history of the hexad mul- 

 tiple chromosome answers this question definitely in favor of 

 the latter alternative, for, although joined to another element, 

 the same characteristic features of behavior and distribution 

 mark the accessory chromosome as when it is free. It is incom- 

 prehensible that there should be this definiteness of action on 

 the basis of mere chance — such a conclusion is foreign to all our 

 experience with living structures. Taken in connection with the 

 parallelism between the development of sex and sex linked 

 characters, and its distribution during maturation, all the his- 

 tory of the accessory chromosome speaks for specific organiza- 

 tion and self perpetuation. The fact that it \nolates the practi- 

 cally universal rule of a complete division of all the members of 

 the complex in each mitosis in order to accomplish its necessary 

 distribution and self perpetuation is an unanswerable argument 



JOURNAL OF MORPHOLOGY, VOL. 29, NO. 2 



