550 CLARENCE E. McCLUNG 



The number of chromosomes within cells of an organism, he 

 states, is variable, according to the law of fluctuating variations, 

 because the number in any cell is due to the constancy in the 

 amount of chromatin and the median size of the chromatin 

 aggregates. Opposed to this is all the evidence, already given, 

 regarding the high degree of regularity in the Acrididae where so 

 many genera are aUke in number, although the amount of chro- 

 matin varies widely. In this large group, the family, variation 

 is infrequent, but in one species, Hesperotettix viridis, variation 

 is common. Certainly under the terms of Delia Valle's argu- 

 ment the greater variation should occur where there are the 

 greater differences in amount of chromatin. But if there is any 

 truth in the assumption, some variation would be expected in 

 the cells of the individual and this does not occiu- in these 

 Orthoptera. As reported for Culex by Whiting ('17) in the 

 germ cells the diploid number is constantly six, Hance ('17) 

 finds the same conditions generally true of the somatic cells, 

 but Holt ('17), working upon the same material, discovers a 

 range of variation extending from six to seventy-two in certain 

 intestinal cells. It is very clear that the amount of chromatin 

 is here not constant, while the median size of the chromosome 

 remains practically unchanged. There is no correspondence, 

 either, between the size of the nucleus, or of the cell, and the 

 number of chromosomes. No evidences whatever of any bal- 

 anced physical system, such as Delia Valle advocates, appears 

 in these cells of Culex. 



Hertwig's outworn nuclear-plasma relation theory receives 

 just as little support. In H. viridis the amount of chromatin 

 is much the same in all the cells of a given generation and yet 

 the num^ber of chromosomes in the haploid condition ranges from 

 nine to thirteen. Along with this fixity in the amount of the 

 chi'omatin and variation in chromosome numbers, goes a con- 

 stancy of size series up to certain chromosomes, beyond which 

 there is a sudden change. The phenomena relate to no means or 

 averages, but concern definite morphological entities. In place 

 of fluctuating variations there is definite and determinable 

 order. What happens is explainable, not upon circumstances of 



