404 MITCHEL CARROLL 
may account for the appearance of no. 3 in figures 11, 12, and 
13, which is typical for the extra tetrad rather than for the 
former. The dumb-bell shape without knobbed ends (figs. 1, 4, 
5, 28529) 30; 33; 53}'57, 82, 83) 121, 122-123 and 128) s0nihe 
form seen in figures 58, 59, 60, 61, 86, and 127, together with, it 
seems to me, a trifle smaller size than no. 3, can usually be 
taken as sufficiently diagnostic. Nor can I recall ever having 
certainly observed the extra element in the form of a ring as 
sometimes happens with no. 3 (figs. 129, 180). 
I have not attempted to test no. 3 and the supernumerary 
tetrad metrically, because the difference between these two is 
small enough to fall within the limits of error in the drawings. 
Then, too, it should be possible to demonstrate more conclu- 
sively by a study of the early growth stages and by breeding the 
animals, if these two elements are genetically related. It is 
obvious that if the extra tetrad is a duplicate of a member of the 
normal chromosome group, that member is no. 3. 
The triploid extra homologues. In a few follicles, 980 E and 
2511 D and IJ, there are three extra dyads present. Spermato- 
gonial metaphases of complexes containing these three are shown 
in figure 41, plate 4, and figure 64, plate 7. In the first sperma- 
tocyte metaphases (pl. 6, figs. 52, 53, 54, and 55) two of these 
dyads synapse to form a typical tetrad, while the third remains 
free. The latter passes undivided to one or the other pole. 
In the drawings, if it is going toward the same pole as the acces- 
sory, it is placed above the extra tetrad, if to the opposite pole, 
below the tetrad. All three dyads are seen to be homologues of 
the extra dyad first described and consequently of each other. 
Second spermatocytes derived from such complexes, containing, 
respectively, twelve, thirteen, and fourteen dyads, are illustrated 
in figures 37, 38, and 35 of plate 4. 
The pairing of the triploid supernumeraries is somewhat anal- 
ogous to the probable behavior of the three sex chromosomes in 
XX Y females in Drosophila (Bridges, ’16). It seems that any 
two of these may synapse, but the two X’s more often pair than 
an X with a Y. 
