AN EXTRA DYAD AND EXTRA TETRAD IN CAMNULA 401 
condition, to a less degree, can be seen in the supernumerary 
tetrad in figure 3, plate 1; figure 72, plate 8, and figure 135, plate 
14. Euchromosome no. 3 exhibits similar but greater variations, 
as the plates reveal. Some of these variations in size are undoubt- 
edly due to the technique employed. 
All the supernumerary elements, then, in this material, whether 
paired or unpaired, when judged by the usual criteria of size 
and form, are evidently genetically related. 
The extra dyad. Spermatogonial complexes containing un- 
paired supernumeraries are illustrated on plate 10 (figs. 96, 98, 
99, 101). So far as I have been able to observe, such unpaired 
elements divide in the spermatogonial mitoses like any other 
chromosomes, as is presumably the case for all supernumeraries 
hitherto reported. For, since they are found in all the first sper- 
matocyte cells of individuals in which they occur, all the extra 
chromosomes so far reported (Wilson, ’05, ’07 a, ’07b, ’09 a, 
09 b, ’10; Stevens, ’08, ’712a, ’12b; Carothers, ’17; Wenrich, 
17; McClung, ’17; Robertson, ’17) must divide in every sperma- 
togonial mitoses. But when dealing with such variable ma- 
terial as Camnula, one is scarcely justified in making such a 
positive assertion without more extended observations than I 
have yet made. 
In the postspireme stage of the first spermatocyte the 
unpaired element is somewhat precocious. It behaves in this re- 
spect like the accessory, condensing and contracting ahead of the 
euchromosomes (pl. 12, figs. 118 and 119). But it exhibits no 
tendency to synapse with the accessory. 
In the first spermatocyte metaphase the unpaired extra dyad 
is a Short rod and lies horizontally in the equatorial plate with one 
of its two chromatids directly above the other (pl. 3, fig. 26; 
pl. 8, figs. 79 and 80; pl. 9, fig. 92; pl. 10, fig. 93) as in a sperma- 
togonial metaphase. A spindle fiber is typically attached at 
one angle (pl. 1, figs. 7 and 10; pl. 6, fig. 54), at doubtless the 
point of attachment for one of the fibers in spermatogonial 
mitoses. Usually the dyad passes undivided to one pole preced- 
ing the division of the euchromosomes (pl. 11, figs. 105, s, and 
106, s). Rarely (pl. 8, fig. 79) spindle fibers are attached at both 
