jMETAPHASE spindle in FORFICULA ATJRTCTJLAR[A. 253 
figs. 1, 4 and 5, and the latter in figs. 2 and 3. I have 
failed to discover which arrangement is normal. 
i ig. 6, PI. 11, is a lateral view of the equatorial plate in a 
late ' secondary spermatocyte metaphase, and the bivalent 
chromosomes are seen to be undergoing constriction. This 
stage therefore immediately precedes that with which we 
propose to deal. The centrosomes of this cell are shown at a 
magnification of 889 diameters in fig. 49, PI. 17, and the 
distance between them, estimated from this magnification, is 
7'8^. Fig. 7, PI. 17, shows the equatorial plate at the con- 
clusion of the metaphase ; constriction is here seen to be 
complete, and the dyads have become resolved into pairs of 
univalent chromosomes, which are ready to pass towards the 
two poles. Fig. 50, PI. 17, shows the centrosomes of this 
cell, and the amount of their divergence is found from the 
drawing to be 8T fx. Figs. 8, 9 and 10, Pi. 17, are drawings 
of the equatorial plate in three cells undergoing successive 
stages of the anaphase, and the daughter-chromosomes are 
observed to be moving further and further apart. The centro- 
somes of these cells are represented in figs. 51, 52 and 53 
respectively, and the distances between them, estimated from 
the known magnification, are 8’3, 8‘5 and 8 7 /,<. 
Consideration of the drawings of these five cells suggests 
that the length of the spindle at the moment when constric- 
tion of the chromosomes is complete is a constant for this 
mitosis of the individual. It is reasonable to suppose tlmt, if 
fixation had been delayed until the centrosomes of fig. 6 
were 8T jx apart, the appearance of the chromosomes would 
have been similar in every respect to that seen in fig. 7 ; 
and we must likewise suppose that the equatoi*ial plate in 
figs. 8, 9 and 10 was identical with that of fig\ 7, when the 
length of the spindle in these three cells was 8‘1 /.<. We will, 
however, check these results by making drawings of a second 
set of five cells in which the distances between the centro- 
somes are respectively 7*8, 8*1, 8*3, 8*5 and 8*7 fi. Figs. 11 
to 15, PI. 17, are lateral views of the equatorial plate of these- 
cells, and each is seen to correspond exactly with the drawing 
