AN EXTRA DYAD AND EXTRA TETRAD IN CAMNULA 403 
The supernumerary tetrad. A pair of dyads, the homologues 
of the unpaired element just described, is present in the sperma- 
togonial complexes of a number of follicles in the atypical indi- 
viduals (pl. 4, fig. 40, 42; pl. 7, fig. 63; pl. 10, fig. 97; pl. 14, figs. 
131, 1382, 133). These dyads behave in this generation and in 
the two succeeding ones like any typical euchromosome pair. 
In the late prophases of the first spermatocytes, unlike their 
unpaired homologue, they do not seem to be precocious when 
compared with the euchromosomes. They synapse like any 
other chromosome pair to form a typical tetrad which is not dis- 
tinguished by any pronounced differential behavior. In the first 
spermatocyte spindle this tetrad appears usually as a rod, ex- 
tended parallel to the axis of the spindle, but it may take the 
form of a V (figs. 52, S, 54, S) or a cross (figs. 2, 84, 127, S). 
In this mitosis, there is a slight apparent shift in the points of 
fiber attachment in the two dyads composing the tetrad when 
compared with their unpaired homologue. The fibers seem to be 
attached at the middle points of the polar ends of the two halves 
of the tetrad, instead of at one angle of the end as in the un- 
paired elements. The tetrad divides in metaphase (figs. 27, 72, 
73, 112, 120, 121, 124, 125) in. the typical fashion, the two 
halves passing to opposite poles as V’s in anaphase. These 
halves divide like the rest of the dyads in the second spermato- 
cyte mitosis (figs. 69, 70, 71, 104, 116, 138, 139). 
A comparison of the extra tetrad and euchromosome no. 3 on 
plates 1, 2, 3, 6, 8, 9, 18, and figure 135 on plate 14 shows what a 
close resemblance there is between these two in size and form. 
In figures 3, 72, 120, and 185 there are even indications of the 
knobs, so often seen on the ends of no. 3, in the supernumerary 
tetrad. No. 3 in figures 11, 12, 138, and 22 could not be distin- 
guished from the extra tetrad, were the latter present in these 
complexes. In figures 128, 124, and 125 I am not sure that the 
two elements have been properly identified. Yet, in spite of this 
close resemblance, it is possible, I think, in the majority of cells, 
to distinguish between these two chromosomes. All the chromo- 
somes in 954.1 are more condensed, probably on account of the 
killing agent employed, than in the other animals. This fact 
