270 WM. EEES B. ROBERTSON 



somes, descent by variation from a common ancestral series of 

 chromosomes may certainly be inferred, and the degrees of varia- 

 tion shown in these chromosomes is paralleled by the degrees of 

 variation exhibited by somatic structures, which systematists 

 have made use of in showing the relationship of species, genera, 

 subfamilies, etc. 



Variations which have occurred in the Acrididae and which 

 seem to be of a permanent nature are the fusion of non-homol- 

 ogous autosomes to form compound chromosomes as in the 

 species of the genus Chorthippus. That these are variations 

 is to be inferred from the fact that about nine-tenths of the 

 genera of the twenty-three-chromosome grasshoppers do not 

 possess these V's, while in one-tenth, and especially this one 

 genus Chorthippus, the species so far described (5) all show this 

 variation. It is interesting to note that it occurs in both the 

 American and the European species of the genus. In Hespero- 

 tettix jMcClung ('05) has described a somewhat similar occurrence, 

 though here the sex chromosome is concerned. The variation 

 is constant for all species of the genus that have been examined. 

 Likewise in the genus Mermiria McClung ('05, '14) has de- 

 scribed associations similar to Hesperotettix but in which tivo 

 autosomes seem to be linked up permanently with the sex 

 autosome. 



In Jamaicana we have a third case of such chromosome varia- 

 tion, which, however, is peculiar in that two variations, each 

 apparently permanent, exist side by side within the same ani- 

 mal, as the compound V paired with its rod-mates seems to 

 show. The associated rods evidently remain together through 

 spermatogonial and first and second spermatocyte generations, 

 and are found even in somatic cells, while their rod-mates remain 

 separate. This case is of great importance for it shows that 

 chromosome variations characteristic of two classes of individual 

 animals may exist side by side within the same cell, apparently 

 independent of each other, conditions we should expect to find 

 in the cells of hybrid animals. 



These, it seems to me, are permanent variations of a funda- 

 mental type; but in addition to these, I have described in the 



