568 CLARENCE E. McCLUNG 



The significance of the form of V-chromosomes, as an indi- 

 cation of multiple constitution, is bound up intimately with the 

 question of numbers. ,Only when the limbs of the V, counted as 

 units, with the rod chromosomes, total the number characteristic 

 of the family can there be such evidence of multiple constitution, 

 according to the terms of Robertson's argument. If it appears 

 that such elements exist under other circumstances, then it is 

 necessary to assume that there may be more than one type of V. 

 This Robertson does and uses as a criterion for the V, indica- 

 tive of multiple composition, the presence of a distinct achro- 

 matic bridge at the apex of an acute angled structure. The final 

 test of the validity of his generalization becomes therefore a 

 structural one. There is no doubt of the accuracy of his deter- 

 mination of such a condition and he has with great care traced 

 it through all the stages of maturation. It is unfortunately 

 true, however, as Carothers and Wenrich have shown, that 

 equally clear non-staining bridges occur in atelomitic chromo- 

 somes of Trimerotropis where the full complex of twenty-three 

 is present. Conversely, in cases where undoubted combina- 

 tions exist, as in H. viridis, no distinct achromatic bridges at 

 the point of fiber attachment appear. This seems to be true 

 of Jamaicana also, judging by the figures of Woolsey and of 

 Robertson himself. It seems certain therefore that the V-form 

 of chromosomes, is, in itself, no indication of a multiple condi- 

 tion. If this be true for the Acrididae it is quite useless to 

 consider its value in other groups where the chromosome con- 

 stitution is less well known. 



The form of certain first spermatocyte chromosomes and the 

 behavior of their parts in this mitosis is regarded by Robertson 

 as further confirmation of his belief in their multiple character. 

 He draws a close parallel between them and free ■ elements of 

 other species through homologies of size and form. Since the 

 limits of these supposed elements are fixed by the achromatic 

 bridges at the point of fiber attachment, their validity as tests 

 for chromosome boundaries is questioned for the same reasons as 

 were given above. I should however like to speak more at 

 length regarding this form of chromosome — the double rings. 



