140 
Digby. — On the Arckespoj'ial and 
threads associate more and more closely and concentrate, and thus gradually 
constitute the entire univalent spireme (filament) which eventually segments 
transversely into the univalent chromosomes. The approaching threads are 
precisely similar, even to the correspondence of their beading. Later it will 
be seen that this same phenomenon is exhibited by the threads or asso- 
ciating halves of univalent spireme in the presynaptic and synaptic phases 
(PI. IX, Figs. 41 and 46) and by the filaments or conjoining entire univalent 
spiremes in the stages preparatory to second contraction (PL X, Fig. 69). 
The linin threads become increasingly distinct, and the chromatic beads 
more definitely arranged, often forming groups of four (PL VIII, Figs. 12 
and 13). Gradually the chromatin infiltrates the linin threads, causing them 
to stain chromatically (Figs. 14 and 15). Lengths of threads become 
closely apposed in pairs (Fig. 16), and the several paired portions (fila- 
ments) incline to segregate in a form suggestive of the future individual 
chromosome segments. In some of these paired segments (filaments) the 
two sides (threads) may be still beaded and separate for a distance, then 
becoming closely associated to form a thickened rod — the future chromo- 
some (Figs. 17 and 18). Fine strands still connect the various segments. 
In the next stage there is an almost complete approximation of the parallel 
sides (threads) (Fig. 19); the space between them, when visible, is to be 
distinguished as the line of fission which will separate the daughter chromo- 
somes on the approaching spindle. The spireme filaments, i.e. the entire 
univalent spiremes formed by the association of threads in pairs, are some- 
what slight and curve and twist, and the chromatin is evenly diffused 
throughout their lengths. In some of the nuclei the fission is more evident 
than in others (Fig. 20). 
As the nuclei approach the spindle stage, the filaments become 
increasingly individualized as chromosomes ; one or two nucleoli may still 
persist. Spindle fibres appear in the cytoplasm and converge towards the 
nucleus from four points (Fig. 21). These phases are evidently exceedingly 
quickly passed through, and even in two adjacent nuclei one of them may 
be in a stage such as shown in Fig. 19, while the other maybe in metaphase. 
With the disappearance of the nuclear membrane, and the invasion of the 
spindle fibres, the chromosomes concentrate and consequently thicken, and 
vestiges only of fission can be discerned (Fig. 22). In the process of arrang- 
ing themselves on the spindle (not figured) the chromosomes are still 
elongated, but when adjusted they speedily thicken and stain deeply 
(Fig. 23). The line of fission then opens out and separates each chromo^ 
some into its daughter halves, and these recede to their respective poles 
(Fig. 24). In anaphase (Fig. 1) there is little visible indication of the 
separation of the halves (threads), preparatory for the next division, inasmuch 
as fission does not appear until late anaphase or early telophase (Fig. 2). 
This feature contrasts with the spindle figures of the homotype, where fission 
