460 E. ELEANOR CAROTHERS 



number 5 because of their similar size and because not more 

 than one in any individual varied from the Hippiscus form 

 until I reached individual number 31 (plate 5). Here all of 

 the chromosomes are either of the Stenobothrus type or J's ex- 

 cept numbers 1 and 2 and they are too small for any confusion. 

 Number 1 is freely of either type, so that we should expect to 

 find, if a sufficient number of animals were studied, some with ten 

 tetrads of the Stenobothrus type. The nearest approach to this 

 possibility in these sixty-two specimens is the occurrence of eight 

 in individual number 6 (plate 2). On the other extreme, it has 

 already been noted that three rings and the accessory are atelo- 

 mitic throughout. This would leave a possibility of eight telo- 

 mitic tetrads. Individual number 62 (plate 9) is of this composi- 

 tion. 



Plates 2 to 5 present quite a different appearance from plates 

 6 to 9, for the former group has many more chromosomes with 

 nonterminal fiber attachment than the latter. The results are 

 recorded in the order in which the animals were collected, which 

 was also the order in which they were studied. The individuals 

 represented on plates 2 to 5 were taken in the Yosemite Valley; 

 Sisson, Cal. ; and Eugene, Ore. Those represented on plates 6 to 

 9 are from Friday Harbor and Olga, Wash. ; La Grande, Ore. ; and 

 Pocatello, Ida. They grouped themselves as shown without the 

 slightest rearrangement. I refer to the first group as form A and 

 to the second as form B. 



The following table, made up from the plates, gives the total 

 number of atelomitic and J-shaped tetrads. The first and third 

 columns represent form A and the second and fourth columns 

 represent form B. Each horizontal row, therefore, represents 

 two individuals. The first horizontal row represents individual 

 number 2 (plate 2), form A, in columns 1 and 3, and individual 

 number 33 (plate 6), form B, in columns 2 and 4. The suc- 

 cessive horizontal rows represent successive individuals in the 

 two forms, i.e., numbers 3 form A, and 34 form B in the second 

 row, numbers 4 form A, and 35 form B, in the third row, etc. 



The ratio of atelomitic to J-shaped tetrads in the case of form 

 A is 0.42; in the case of form B, 0.47. One might have expected 

 in place of this relatively constant relation that the larger num- 



