Meiotic Mitoses of Osmunda. 163 
These phases clearly demonstrate the dual nature of each univalent chromo- 
some, which presumably persists throughout the cycle of chromosome disso- 
lution and reconstitution (see Text-fig., Nos. 1-8). 
In late anaphase the substance of each chromosome is seen to be 
divided already into longitudinal halves — the ‘threads’ (PI. VIII, Fig.. 2). As 
the newly formed nucleus proceeds towards rest, the chromosome halves or 
threads become beaded (Fig. 4). The threads gradually separate widely, 
and the beads become resolved into finer and finer granules until a fine 
reticulate state is reached— the so-called resting stage (Fig. 6). 
During prophase the series of events is reversed, and the chromosome 
halves, or threads, reassociate to build up the univalent chromosome. The 
first indication of the coming together of the halves consists in the drawing 
together, in parallel pairs, of the fine beaded threads (Fig. 11). Each 
beaded thread gradually concentrates into spireme (Fig. 16), and the asso- 
ciation of the two halves (i. e. the two threads) becomes increasingly intimate 
until it results in the organization of the completed univalent chromosome 
(Fig. 21). The space between the associating halves (threads) forms the 
future line of fission which splits the chromosome into its daughter halves 
on the equatorial plate. 
The daughter chromosomes proceed to their respective poles (Fig. 24), 
and in late anaphase (Fig. 2) each divides again by fission into longitudinal 
halves (threads), thus completing the cycle. 
3. Interkinesis betzveen the Telophase of the Last Archesporial 
Division and the Heterotype Prophase. 
The telophase of the last archesporial division (PI. VIII, Fig. 25) is in- 
distinguishable from that of the preceding archesporial telophases, and 
shows the longitudinal splitting of the chromosomes into threads (see Text- 
fig., Nos. 9-12). The late telophase (Fig. 29) may pass through an inter- 
kinetal rest (PI. IX, Fig. 34), or it may proceed directly into the heterotype 
prophase (Fig. 36) (see Text-fig., Nos. 13 and 14). 
Those nuclei which pass through an interkinetal rest show the same 
gradual formation of a reticulum by the spreading out of the threads and 
the fragmentation of the chromatic granules, as in the archesporial divisions. 
Those nuclei that proceed directly from telophase into the heterotype pro- 
phase show transitional stages in which both telophase and prophase 
characters are present (Figs. 30, 32, and 33). There is no complete separa- 
tion of the threads or chromosome halves, but traces of paired spireme and 
paired beads persist from the one phase to the other. These, therefore, 
substantiate the identity or homology existing between the parallel threads 
of the telophase (PL VIII, Fig. 25) derived from the longitudinally split 
chromosomes, and the parallel threads of the heterotype prophase 
