CHROMOSOME STUDIES 261 



the chromosomes we have structures sufficient in many respects 

 to serve as a morphological basis for the phenomena of heredity, 

 variation and evolution. 



In the first place there is a number which may be considered 

 fundamental and constant, not only for all the cells of an indi- 

 vidual but likewise of the individuals of a species, the species of 

 a genus, the genera of a subfamily and, if they are sufficiently 

 closely related, even the subfamilies of a family, as may be seen 

 in the Truxalinae, Oedipodinae, and Acridiinae, three of the four 

 subfamilies of the Acrididae or better in the subfamilies of the 

 Tettigidae. In the family Tettigidae, with the exception of 

 three specimens,'^ I have found this number to be 13 (cf) and 14 

 ( 9 ) for the genera I have so far examined : Choriphyllum (one 

 species) Nomotettix (one species), Acridium (four species) , Parat- 

 tettix (two species), and Tettigidea (two species) 



This number I found in all cells, both germ and somatic; 

 in the testis, spermatogonia and first spermatocytes, in the hy- 

 podermis, the integument, the proctodeum, the mid-intestine, 

 'fat body,' muscle tissue, the follicular walls of the gonads (cf 

 and 9). In the 'fat body' two cells were seen which showed 

 instead of the usual number (13) the double number (26). This, 

 however, may be the result of failure of the cytoplasm to divide. 

 I have no hesitation therefore in saying that the numbers fun- 

 damental for the family Tettigidae are 13 (cf) and 14 ( 9), i.e., 

 six pairs of autosomes plus the sex chromosomes. 



In the three subfamilies of the Acrididae (Truxalinae, 

 Oedipodinae, Acridinae), over forty genera (McClung '14) so 

 far examined have been found to possess with three exceptions 

 twenty-three chromosomes. The exceptions are in the genus 

 Chorthippus (Stenobothrus) , where in five species seventeen 

 chromosomes have been reported, and in material from an 

 unidentified specimen described by McClung ('14^ figs. 59-76) 

 as having twenty-one. My work upon Chorthippus curtipennis 



= The three exceptions were one individual (c?') in which there occurred a 

 deficient supernvunerary sex chromosome, and two others (cf and 9 ) in which 

 there seemed to be the one-and-one-half equivalent of supernumerary no. 1. 

 chromosome attached to a normal no. 1 (figs. 136 to 147 and my Studies III). 



