Studies on Chromosomes 187 



and that this may be one way in which their progressive accumu- 

 lation in number in successive generations is held in check. 



For the foregoing reasons it cannot be said that any of the rela- 

 tions described appear with absolute uniformity or fixity. The 

 condition typical of each individual must be discovered by the 

 study and comparison of large numbers of cells. I will only say 

 that prolonged and repeated study has thoroughly convinced me 

 that the relations, as described, may be regarded as being on the 

 whole individual constants. This judgment is based primarily 

 on the exhaustive study of a few of the best series of preparations 

 of individuals of the 21, 22, 23, and 26-chromosome types, in 

 which the facts are quite unmistakable and have given the point 

 of view from which the less favorable material of other cases may 

 fairly be examined. 



D DISCUSSION OF RESULTS 



The principal significance of these phenomena seems to me 

 to lie in their bearing on the general hypothesis of the "individual- 

 ity" or genetic continuity of the chromosomes; but they are also 

 of interest for a number of more special problems which I will 

 first briefly consider. 



The Relation of the Chromosomes to Sex-production in Metapodius 



The conditions seen in this genus seem to be irreconcilable with 

 any view that ascribes the sexual differentiation to a general quanti- 

 tative difference of chromatin, whether expressed in the number or 

 the relative size of the chromosomes. In all known cases of constant 

 sexual differences in the chromosomes it is invariably the female 

 that possesses the larger number of chromosomes or the greater 

 quantity of chromatin, 10 and this has naturally suggested the 

 view that this difference per se may be the sex-determining factor. 

 As I have pointed out before ('09), such a view is inapplicable to 

 cases like Nezara or Oncopeltus, where the idiochromosomes are 

 of equal size and no quantitative sexual differences are visible; 

 yet the phenomena in these genera are otherwise so closely similar 



10 See review in Wilson '09. 



