472 E. ELEANOR CAROTHERS 



varying from animal to animal. Specimen number 74 with its 

 fourteen atelomitic chromosomes (plate 11, 74) was taken in 

 the Yosemite Valley, hence should belong to the group having 

 the larger number. The other two are from Puget Sound, where 

 we would expect the smaller number. One has ten (plate 11, 72) 

 and the other, much to my surprise, has eight (plate 11, 73), 

 which, if my conclusion that three of the atelomitic rings are 

 constant is correct, would be the minimum number for the fe- 

 male, since she possesses two accessories, giving a complex of 

 twenty-four chromosomes instead of twenty-three as in the male. 

 We may now answer the third and forth questions propounded 

 at the beginning of this paper. The complex is constant for 

 any given individual but varies within fixed limits for the 

 species. Hence there is no need to assume any regulatory mech- 

 anism during maturation or fertilization. 



3. Second spermatocytes 



a. Types found in individual number 1. As has already been 

 noted, the formula, 2™, in which n represents the number of 

 pairs of chromosomes under consideration, gives the possible 

 combinations in the gametes. According to this formula ani- 

 mal number 1, as we have seen "on page 455. would be expected 

 to form sixteen sorts of second spermatocytes. However, as 

 we can not distinguish between chromosomes 7 and 8 ; we can 

 identify only twelve sorts, as shown on plate 12. Numeri- 

 cally, they fall into two classes, those with eleven (figs. 

 1 j to o) and those with twelve chromosomes (figs, p to u), owing 

 to the presence or absence of the accessory. In the class with 

 eleven chromosomes we would always have the four atelomitic 

 chromosomes derived from the four Stenobothrus rings (fig. 

 lj). In addition we may have one of the larger atelomitic 

 dyads (fig. k), the small atelomitic dyad (fig. I), the small 

 atelomitic dyad and one of the large ones (fig. m), both large 

 ones without the small (fig. n), or the atelomitic dyads of all 

 three (fig.o). Figures p to u present a similar series, except that 

 they each have one more atelomitic dyad, the accessory. 



