MULTIPLE CHROMOSOMES 583 



his results it would appear that all chromosomes are, in a sense, 

 multiples, and it is conceivable that these parts might be vari- 

 ously associated, producing even extensive numerical variation, 

 still without loss or gain of essential structural elements. 



The peculiar case of Ascaris megalocephala, where evident 

 multiple chromosomes are retained intact in the germ cells while 

 they suffer fragmentation in the somatic cells, is an extreme in- 

 stance of numerical variation which occurs in one individual. 

 How common such relations may be we do not know, since so 

 little has been done in the study of the complete history of a 

 single organism; but it is ob\dous that the Orthoptera stand at 

 the opposite extreme from Ascaris in the persistence of chi'omo- 

 some organization, for here all the cells of an indi^ddual seem 

 to be invariably the same, and the indi\'idual is representative 

 of the group. But even in this stable assemblage we encounter 

 the conditions which I have described for H. viridis. This 

 case, with its diminution in number, and that of Culex, with its 

 great increase, are alike in the fact that the measures of differ- 

 ence are entire chromosomes and not parts of such, as seems to 

 be the case in Ascaris, unless indeed these chromosomes be 

 multiples of a high order of complexitj^ 



If it were possible for chromosomes to reproduce themselves 

 and still preserve their physical configuration unchanged, there 

 would probably be little question of their continuity and indi- 

 viduality — the demonstration would be self evident. But it 

 happens that the necessities of the case requu'e that each newly 

 produced chromosome should take part in the formation of a 

 new nucleus, tlirough whose activities the cell as a whole and 

 each chromosome, individually, is enabled to restore the volume 

 diminished by the act of division. During this process the out- 

 lines of the chromosomes become materially changed and in 

 their extreme diffusion can no longer be traced in many cases. 

 Because of our limitations in observational power they appear 

 to be lost as separate individuals and we are thus deprived of 

 the simple test of observed continuity. Later, in the same cell, 

 there reappears a series of chromosomes severally like those which 

 seemed to disappear during the period of metabolic activity. 



