464 E. ELEANOR CAROTHERS 



they show no exceptional conditions. Data from these twenty 

 are used in the broken curve of form B, which includes all of 

 the specimens of this form in my collection. 



Analysing these curves we see that in form A the extreme 

 numbers of atelomitic dyads are 15 and 9, the mode 12 and the 

 mean 12.3. In form B the extremes are 11 and 6, mode 7 and 

 mean 8. It will be noted that the extremes in neither group 

 reach to the mode of the other. The graph of form A is well 

 balanced, indicating a stable group with considerable range of 

 variation. That of form B, while showing much less variation, 

 is skewed to the left, which would lead one to suspect that this 

 group is changing towards the more stable form. 



Plates 6 to 9 show chromosomes number 3 and number 5 always 

 of the Hippiscus type in form B, though both are subject to change 

 in form A. There is some question as to whether chromosome 

 number 5 is always correctly identified. However, it is clear 

 from animal number 60, which has three rings of the Stenobothrus 

 type and five J-shaped tetrads, that eight tetrads have the poten- 

 tiality of being atelomitic. It is puzzling that five (animal no. 

 47) is the nearest approach to this extreme found. Animal num- 

 ber 60 with its possibility for eight Stenobothrus rings offers 

 one of the strongest indications that these two groups may be 

 really members of a single species. 



c. Segregation and recombination of ho?nologues of J-shaped 

 tetrads in eleven individuals of Circotettix lobatus. Eleven speci- 

 mens of this species were taken in a very circumscribed area at 

 La Grande, Ore. and a single specimen of another species (rabula) 

 at Ogden, Utah. This latter animal had both telomitic and 

 atelomitic chromosomes, but no J-shaped tetrads. This is not 

 significant, however, as three of the eleven individuals of lobatus 

 also lack J-shaped tetrads. 



First spermatocyte complexes of eight of the eleven lobatus are 

 shown (plate 10). The other three are included in the descrip- 

 tion. As just stated, three (or over one-fourth) of these animals 

 have no J-shaped tetrads. Four have one and the remaining 

 four have two. As in Trimerotropis, their dyads segregate at 

 random in regard to each other and to the accessory. 



The minimum of atelomitic tetrads in -this limited collection 



