Wilson. — Spermatogenesis in the Bryophyta. 425 
between the reconstituting nuclei in the early telophase was found to be 
much more constant; and here the results were as follows : — 
Distance between daughter nuclei at telophase of last division, about 6-3 fx. 
Distance between daughter nuclei at telophase of penultimate division, 
about ic-6 ix. 
Distance between daughter nuclei at telophase of antepenultimate division, 
about 1 2 fx. 
The importance of a method by which the ages of the various anthe- 
ridia can be determined is made apparent by a consideration of the conclu- 
sions arrived at by J. and W. Docters van Leeuwen-Reijnvaan (41, 42). 
These investigators, who have described the spermatogenesis of several 
species of Polytrichum and of Mnium sp., state that, in all these plants, 
centrosomes are constantly present at the divisions in the antheridium. At 
the final division a reduction takes place whereby the haploid number of 
the chromosomes is reduced to half, in Polytrichum sp. to three, and in 
Mnium to four. Arens (2), who had previously examined Polyirichum 
juniperinum and Mnium hornum , found that the final division in these 
species was of the normal type. The later divisions in Mnium hornum 
were therefore examined with especial care. 
During the early stages of the penultimate division a body is cut off by 
constriction from the nucleolus, although, as previously pointed out, nothing 
of this kind has been discovered in the earlier divisions. The course of 
events is the same as those previously described in the reduction division of 
this plant, where a similar process takes place. A small bud-like outgrowth 
is developed on the nucleolus (PI. XXXVII, Fig. 4), and this by constric- 
tion is finally separated off, the body so produced lying close to the nucleolus 
within the nuclear membrane. This body has not been discovered outside 
the nucleus, and as it has not been seen during the later stages of division, 
it probably soon disappears. 
During the prophase of the final division a somewhat similar process 
takes place, but here two bodies are produced. The nucleolus becomes 
slightly elongated and dumb-bell shaped, then by further constriction almost 
complete division into two spherical masses is effected (Figs. 6 and 8). 
Before complete separation, however, one of these masses buds off a com- 
paratively small spherical body similar to that already described in the 
penultimate division (Fig. 7). The three bodies ultimately become free, but 
for some considerable time lie close together in a row within the nucleus. 
As before, these have not been seen to pass beyond the membrane, and 
no trace of such bodies has been discovered in the cytoplasm. 
In view of these occurrences the statements regarding the origin of the 
centrosome made by J. and W. Docters van Leeuwen-Reijnvaan (41,42) must 
be considered. According to these observers the centrosomes in Polytrichum 
