AN EXTRA DYAD AND EXTRA TETRAD IN CAMNULA 399 
in a spermatogonial, a first spermatocyte, and second spermato- 
cyte cyst. The spermatogonial complexes (cyst 10; figs. 99 and 
101) of twenty-four dyads are constituted as follows: eleven 
pairs of chromosomes plus the accessory plus a supernumerary 
dyad; this organization in the first spermatocyte metaphases 
(cyst 9, figs. 77 and 106) takes the form of eleven tetrads plus one 
accessory plus one extra dyad. The three expected classes of 
second spermatocytes for this follicle contain, respectively, 
eleven, twelve, and thirteen dyads. Since only six counts were 
secured in cyst 11, it is not surprising that the eleven-dyad class 
was not found. The anaphase with twelve monads going to one 
pole and thirteen to the other results from the fact that occa- 
sionally the odd dyad divides in the first, instead of the second 
mitosis. 
The data so far presented, then, indicate: In five animals from 
islands in Puget Sound there is variation in the fundamental 
numerical organization of the germinal chromosome group within 
the individual. But with one possible exception in cyst 13 of 
individual 2511, the organization of the metaphase complex 1s 
constant for the cyst, save for the classes of second spermatocytes 
resulting from the customary segregation of elements in the first 
maturation division. The chromosome number is constant also 
for the follicle until after the first spermatocyte mitosis. The 
variations in the chromosome groups within the atypical indi- 
viduals are due to the presence of an unpaired extra dyad, to a 
pair of extra dyads, or to both, in certain follicles of the gonads 
of these animals in addition to the elements of the normal 
complex. 
C. The extra or supernumerary elements 
In first spermatocytes there is usually no difficulty in distin- 
guishing the supernumerary elements. A comparison of the 
complexes of normal individuals (pl. 2, figs. 11 to 14; pl. 5, figs. 
43 to 45) and the normal chromosome groups (figs. 21, 22, 23, 31, 
87, 88, 89, 90, and 95, pls. 3, 4, 9, and 10) in aberrant indi- 
viduals, wth the atypical complexes (figs. 1 to 10, 24 to 30, 32, 
33, 92 to 61, 72 to 86, 91, 92, 120 to 130, pls. 1, 3, 4, 6, 8, 9, and 
JOURNAL OF MORPHOLOGY, VOL. 34, NO. 2 
