MULTIPLE CHROMOSOMES 531 



it was not until the discovery of the J-shaped chromosome in 

 Trimerotropis by Miss Carothers that any explanation, consistent 

 with the other known conditions in the group, was made possible. 

 Meanwhile I had accumulated an extensive series of specimens 

 and had studied the complex of the female and needed only the 

 conception of the J-shaped tetrad to bring all the observations — 

 with the exception just mentioned — into conformity. 



In Mermiria, as in Hesperotettix, the fixity of combinations 

 which seem.ed to mark the genus has failed to prevail throughout 

 all its species. While such vai'iation as is shown by H. viridis 

 does not obtain in any species of Mermiria studied, multiples 

 are lacking in texana and neomexicana. These results empha- 

 size strongly the necessity of an extensive series of specimens in 

 any investigation — a requisite I have always appreciated and 

 sought to meet. Our recent work in the Orthoptera has shown 

 that numbers of considerable magnitude are required for extensive 

 generalizations. 



Mermiria hiviitata 



It is not my purpse in the present paper to enter into a com- 

 parative history of the chromosomes in the various species of 

 Mermiria. I wish merely to consider the multiple chromosome 

 found in bivittata, with its modifications in certain groups of 

 individuals which seem to have specific value. My former re- 

 port on this species stated that the multiple chi'omosome con- 

 sisted of two tetrads joined to the accessory chromosome. This 

 is a mistake the occasion for which is discussed elsewhere. More 

 extended study upon a large series of specimens has shown that 

 in this genus, as in Hesperotettix, there is a hexad multiple in- 

 stead of a decad. While there is a striking difference in con- 

 figiu-ation of the element in the two groups, it is due entirely 

 to the form of tetrad involved. In Hesperotettix this is an ordi- 

 nary extended rod with the accessory chromosome joined at 

 approximately a right angle on one end. Mermiria has, on the 

 contrary, a tetrad alread}'^ of just this shape, to the straight end 

 of which the accessory chromosome unites. Thus, while the 

 composition is the same, the appearance is very unlike. How 



