METAPflASE SPINDLE IN FORFICULA AURICULARIA. 
255 
equatorial plane. The complex again appears to be composed 
of a ring ol‘ nine or ten chromosomes with three or two respec- 
tively lying within it; figs. 21, 22 and 25 represent the latter 
arrangement, and figs. 23 and 24 the former. I haVe again 
failed to discover which arrangement is nortnal. 
Figs. 26 to 29, PI. 17, are drawings of the equatoral plate of 
four cells of which the ceiitrosomes, represented at a magni- 
fication of 889 diameters, are given in figs. 64 to 67, PI. 17. The 
di-awings on PI. 17 clearly show that constriction of the tetrads 
has been completed, and that the daughter-chromosomes are 
ready to move apart. The length of the spindle, found from 
digs. 64 to 67, is without exception 10*4 ju; and, since the 
stage of the cells depicted is that with which we are dealing, 
we have reason for supposing that a constant exists also for this 
mitosis. The uneven pair of heterochromosomes is marked 
■X in those cells in which it is visible. 
Let us now measure the spindle length in four more cells in 
order to test the validity of this supposition. Figs. 30 to 33, 
PI. 17, are drawings of the equatorial plate in cells of which 
4he centrosomes are respectively represented by figs. 68 to 71, 
PI. 17. Fig. 30 shows the constriction of the tetrads in pro- 
gress ; fig. 31 shows this constriction completed, as in figs. 26 
to 29; and figs. 32 and 33 show the first divergence of the 
daughter-dyads. The distances between the poles of these 
cells, found from figs. 68 to 71, are respectively 10’2, 10‘4, 10*7 
and 10’9 p, and therefore accord with the length of the spindle 
found for figs. 26 to 29. We must suppose that fig. 30 would 
have become identical with fig. 31, if fixation had not occurred 
until its centrosomes were 10*4 ju apart ; and we must likewise 
suppose that the equatorial plates shown in figs. 32 and 33 
passed through the stage shown in fig. 31, when their spindles 
were of the same length as that of the last named. In the 
circumstances I shall assume that the length of the spindle at 
•the conclusion of the primary spermatocyte metaphase is a 
constant for this species. 
I have found measurements in this metaphase more difficult 
to make than in that of the secondai-y spermatocyte ; for 
