36 W. S. SUTTON. 



some is absent or present. Now twenty-three is the number of 

 chromosomes in the male cells, while twenty-two is the number 

 I have found in the female cells, and thus we seem to find a 

 confirmation of McClung's ' suggestion that the accessory chro- 

 mosome is in some way concerned in the determination of sex. 



Without discussing here the logical consequences of such a 

 conclusion, I will only emphasize the fact that one of the chromo- 

 somes, which in the primary spermatogonia" is scarcely distin- 

 guishable from its fellows, maintains throughout a long series of 

 divisions an indubitable independence ; and finally completely 

 establishes its right to the title of a distinct individual by passing 

 entire to one daughter-cell with the result that no accessory chro- 

 mosome appears in the products of the next division of the other. 

 Taken as a whole, the evidence presented by the cells of 

 Brachystola is such as to lend great weight to the conclusion that 

 a chromosome may exist only by virtue of direct descent by 

 longitudinal division from a preexisting chromosome and that 

 the members of the daughter group bear to one another the same 

 respective relations as did those of the mother group --in other 

 words, that the chromosome in Bracliystola is a distinct morpho- 

 logical individual. 



This conclusion inevitably raises the question whether there is 

 also a physiological individuality, /. r., whether the chromosomes 

 represent respectively different series or groups of qualities or 

 whether there are merely different-sized aggregations of the same 

 material and, therefore, qualitatively alike. 



On this question my observations do not furnish direct evidence. 

 But it is a priori improbable that the constant morphological dif- 

 ferences we have seen should exist except by virtue of more 

 fundamental differences of which they are an expression ; and, 

 further, by the unequal distribution of the accessory chromosome 

 we are enabled to compare the developmental possibilities of cells 

 containing it with those of cells which do not. Granting the 

 normal constitution of the female cells examined and the similarity 

 of the reduction process in the two sexes, such a comparison 



1 McClung, C. E., "Notes in the Accessory Chromosome," Anal. Anz., XX. ; 

 "The Accessory Chromosome, Sex-determinant," BIOL. BULL., III. 



2 A study of the chromosomes of the primary spermatogonia has been made in 

 Melanoplus differentially, a nearly related form in which the later divisions are essen- 

 tially the same as in Brachystola. 



