566 CLARENCE E. McCLUNG 



family, is made exactly normal by counting the limbs of V's as 

 units, (2) the graded size series, sharply broken if the V's are 

 considered as simple .units, is restored if they are compound 

 elements, (3) the form of the univalent chromosomes is so gen- 

 erally a rod in the family that the occurrence of V's, in connec- 

 tion with the circumstances in (1) and (2), is strongly suggestive 

 of multiple constitution. To these should be added the con- 

 formatory evidence of cases like H. viridis which establish on 

 direct observation the principle of chromosome combinations. 



That these circumstances justify the generahzations which 

 Robertson draws regarding the multiple nature of V-chromosomes 

 in general seems much less certain. Because of the great im- 

 portance which attaches to the exact determination of chromo- 

 somal conditions in the germ cells it is essential that our cytologi- 

 cal evidence be most carefully considered. I should like there- 

 fore briefly to indicate where it appears that limits should be 

 placed upon the extension of the principles indicated by condi- 

 tions in Hesperotettix, Mermiria, Anabrus and Jamaicana. 

 Since Robertson has made the widest apphcation of these by his 

 conception of the multiple constitution of V-shaped chromo- 

 somes, an examination of his presentation will illustrate the 

 nature of the difficulties attending such generahzations, into 

 some of which I was myself led. It is fortunate in this con- 

 nection that there is no question regarding the accuracy of the 

 observations. His work is very carefully done and the drawings 

 are clear and definite. 



Agreement has already been indicated with the first two prem- 

 ises of his argument, i e , that the number twenty-three is 

 typical for the family, and that the form of the univalent chro- 

 mosome is a rod with terminal fiber attachment. Like most 

 other biological generalizations, however, these are not without 

 exceptions in the Acrididae. Pamphagus, with telomitic ele- 

 ments, has only nineteen chromosomes and Trimerotropis with 

 numerous and variable V's has a full complex of twenty-three. 

 My unidentified Acridian reported in a former paper ('14) 

 (which may be a species of Circotettix) has nine atelomitic 

 chromosomes in twenty-one chromosomes, while Circotettix, as 



