206 WM. REES B. ROBERTSON 



In T. parvipennis one individual found showed the no. 4 

 chromosomes unequal. In all dividing first spermatocytes 

 these (united) formed an unequal tetrad (figs. 115, 118, 119, 

 120, 122). I infer that the no. 4 chromosome, which came from 

 one of the parents, was originally deficient in size. This char- 

 acter seems persistent enough to be preserved in all the cells 

 of the first spermatocyte found dividing. Moreover, the same 

 deficiency occurs in all the somatic cells studied — the fat-body 

 cells (figs. 104, 105, 108). 



The bearing which these unequal tetrads have upon questions 

 of synapsis and reduction has been discussed in Study III, but 

 will also be considered later in this paper. 



2. Truxalinae (Acrididae) 



In contrast to the family Tettigidae,^ the three subfamilies, 

 Truxalinae, Oedipodinae, and Acridiinae, of the Acrididae, have in 

 general 23 (cf) and 24 ( 9 ) chromosomes. Exceptions to these 

 numbers have been found in Chorthippus (Stenobothrus) by 

 Davis, Meek, and Gerard, and in Hesperotettix and Mermiria 

 by McClung ('05). McClung found Hesperotettix to have 23 

 in the spermatogonia and 11 in the first spermatocyte, and 

 Mermiria to have likewise 23 in the spermatogonia, but only 10 

 in the first spermatocyte. He believed that "the reason for 

 the deviations is due to unusual associations of the spermato- 

 gonial chromosomes in the spermatocytes." I believe that like- 

 wise in Chorthippus we have not 17 chromosomes, but 23, 

 and that here there is a permanent association of certain non- 

 homologous chromosomes, such as no. 11 with 7, no. 10 with 8, 

 or no. 9 with 5, which are not associated in the majority of 

 genera. To show how this may explain the peculiar numbers, 

 I describe first the conditions in Syrbula acuticornis, an example 

 of the 24-23 chromosome genera, in which no such association 

 occurs. 



^ The subfamily Tettiginae should be removed from the family Acrididae and 

 raised to the rank of a family (Tettigidae) coordinate with the Acrididae. 



