496 E. ELEANOR CAROTHERS 
plex). The important point is that there are two small chromo- 
somes in Arphia, instead of three as in Brachystola, and that one 
of these divides equally while the other divides unequally. These 
two small tetrads are very nearly the same size and might easily 
lead a hasty observer who was not familiar with both tetrads to the 
conclusion that they are homologous chomosomes when he ob- 
served them separated as they often are in sectioning and he would 
repeat the statement frequently seen that one of the small chromo- 
somes sometimes divides unequally. The fact is that one partic- 
ular small chromosome always divides unequally in first spermato- 
cyte metaphases of Arphia simplex. 
No indication of a secondary constriction of the larger dyad 
has been observed. 
Dissosteira carolina. Figures 47, 53, 59 and 60 are typical 
first spermatocyte views. ‘The larger dyad is constricted as rep- 
resented (fig. 53), in numerous cases. In this genus it will be 
noticed, however, that the constriction is about the center instead 
of nearer the proximal end, as in Brachystola. One of the large 
tetrads shows a weakness in one chromatid of each dyad, as seen 
in figure 59. This has been found in several animals, and appears 
characteristic of that chromosome, though it does not always 
occur; in this way resembling the constriction found in the larger 
dyad of the unequal tetrad. That this peculiarity marks certain 
chromosomes and always occurs at the same point when distin- 
guishable, is further evidence of the precise arrangement of their 
constituents, whether we consider it to be due to chemical, elec- 
trical or mechanical forces. A suggestive discussion of this sub- 
ject is given by Agar (12). 
4. Second spermatocyte 
Only a very brief period ensues between the first and the second 
spermatocyte divisions, but when the chromosomes become ar- 
ranged in the equatorial plate, one of the small chromosomes is 
again sometimes found associated with the accessory, and, as 
one would expect from a knowledge of the first spermatocytes, 
varies in size, depending, evidently, upon whether the larger or 
