MULTIPLE CHROMOSOMES 553 



phological identity from one generation of cells to the other. All 

 through the spermatogonial divisions each chromosome lies in 

 its own vesicle and can be cle^irly recognized. Recently Wen- 

 rich ('16) has carefully traced certain differentiated chromo- 

 somes in Phrynotettix through much of the history of the 

 maturing germ cells, without loss of their physical identity. In- 

 stead of appearing as ''temporary and variable structures" 

 they are just the opposite, being persistent and exact in or- 

 ganization to the highest degree. Not only are the chromosomes 

 constant in number, but also, and more fundamentally, the 

 chromomeres. Such conditions are probably unknown to Delia 

 Valle and are certainly unappreciated or he could not make such 

 sweeping assertions regarding chromosome instability. 



Perhaps one of the most striking and extensive instances of 

 variation in chromosome numbers yet reported is the one de- 

 scribed by Miss Holt ('17) for the intestinal cells of Culex. 

 Here, in one individual, there may be a range from six to sev- 

 enty-two. Without extending the analysis of the case beyond 

 the simple determination of the numerical conditions, one would 

 be justified in believing that no significance attaches to the 

 mere number of the nuclear bodies. This would follow on the 

 major premise that indefinite and fluctuating variations in 

 numbers are direct evidence of lack of definiteness in organiza- 

 tion. This might presumably be admitted for the somatic cells 

 without entirely invalidating the theory of individuahty so far 

 as it applies to the germ cells, for it is possible that, among other 

 evidences of differentiation in cells, correlative changes in the 

 nature and integration of the chromatin substance might occur. 

 Especially might this be the case in pupal Culex intestinal cells, 

 because these are on their way to disintegration in preparation 

 for the new epithelial lining of the enteron. Meanwhile the 

 germ cells of the species preserve an unvarying constancy in 

 number. But, as Miss Holt shows, the matter is not so simple as 

 it appears. True, there is variation, but it is not indefinite and 

 unordered. There are not always six chromosomes present, 

 but, if more occur, the numbers are multiples of three and repeat 

 in corresponding series the sizes of the primitive complex. Not 



