142 Inheritance and Evolution in Ortlioptera I 



I. IXTKODUCTIUN. 



The well-known cxpeiiments of Mendel, and the work of the Neo- 

 Mendelians with numerous plants and animals, show clearly that 

 surprisingly exact predictions of the results of breeding can be made, 

 provided the gametic constitutions of the parents are known, further- 

 more the gametic constitution of the parents can also be determined 

 by breeding analyses. That there is segregation, or alternativeness, in 

 gametogenesis which accounts for the familiar Mendelian ratios is 

 a generalization which now seems to be well established. However, 

 even in this matter there are some apparently important exceptions 

 which engender doubt in the minds of some persons. 



The existence of unit characters, in the De Vriesian sense, does not 

 appear to have been as clearly demonstrated as that of alternative 

 inheritance, and if one may judge from expressions of opinion con- 

 cerning this matter, the interpretations are at great variance. Thus 

 one group of authors recognize characters in organisms that can be 

 replaced by other characters, when the proper crosses are made — 

 a clear recognition of separable and replaceable characters, which 

 are not necessarily unit characters (1, 3, 8) — while on the other side 

 there are those who believe that the organism as a whole is the only 

 unit and that there are no actual unit characters (9, 7). 



In this paper is presented a preliminary account of an experimental 

 inquiry into the problems of inheritance and evolution, which is now 

 being carried on with several species of the grouse-locusts (Tetriginae) 

 of the genus Paratettix, Bolivar. 



II. Material and method. 



The Tetriginae are widely distributed, and are principally dis- 

 tinguished from other nearly related Orthoptera by the pronotum which 

 extends backwards over the body and wings, a character which varies 

 greatly among the different genera. The North American genera are 

 mostly geophilous, live on damp earth covered with algae, especially in 

 moist meadows and woods, and on the margins of ponds and streams (4). 

 The genus Paratettix, Bol., is distributed over a large part of the United 

 States and Mexico, and the species therein are mainly distinguished by 

 their striking colour patterns. 



