446 
Woodburn.—Spermatogenesis in 
immediately upon the periphery'of the clear surrounding area (Figs. 2 and 3). 
This suggests a supply of material passing from nucleolus to chromatin in a 
plastic condition, not as already formed chromatin granules. 
The Formation of the Chromosomes. 
The condition represented in Fig. 3 passes very quickly over into the 
spireme stage (Fig. 4). By this time the nuclear membrane and also the 
nucleolus have disappeared, and the spireme seems to be loosely coiled 
throughout the nuclear region (Fig. 4). The spireme segments trans¬ 
versely into six chromosomes (Fig. 4 a). Numerous counts were made, and 
while the chromosomes are so small and slender and somewhat intertwined 
in this stage, six seems to be the correct number. Six chromosomes were 
also counted in Polytrichum commune (Figs. 32 and 33). Fig. 31 shows the 
condition of the chromatin in Polytrichtim commune just prior to the stage 
represented in Fig. 32. A spireme is apparently formed, but is much more 
closely wound than in Mnium (cf. Figs. 4 and 4 a with Figs. 31 and 32). 
The chromosomes in Mnium are long and slender as they pass to the poles 
(Fig. 4 b), where they unite again into a spireme condition (Fig. 5). 
Telophases. 
Fig. 5 shows one cell in an early telophase which, judging from the 
size of the antheridium and the fact that the cells are beginning to separate 
and round off from each other, seems to be the last division of the spermato- 
genous tissue. No division that can be termed diagonal occurs in Mnium 
affine , var. ciliaris. The androcytes in their earliest condition are quite 
regularly found lying singly. Occasionally there may be the slightest 
suggestion of a pair. Whereas in the majority of the Liverworts it is quite 
easy to determine, as early as the time of metakinesis, by the position of 
the spindle, whether one is dealing with the last division or an earlier one, 
in the case of Mnium it is much more difficult. My observations lead me 
to believe that the androcytes round off from each other and enter upon the 
succeeding changes quite slowly and gradually until certain stages are 
reached, when, probably due to favourable environmental conditions, the 
remaining phases of transformation are passed through quite rapidly. The 
discussion of the further development of the androcyte will be taken up 
later. A study of the stages represented by Figs. 5 and 6 shows that 
practically the same processes in reverse order occur during the reorganiza¬ 
tion of the nuclei as occurred during the prophases. In Fig. 5 each 
daughter-nucleus has passed over into the spireme stage, while in Fig. 6 
the spireme is giving way to a chromatin network surrounding a nucleolus 
(cf. Fig. 6 with Figs. 1, 2, and 3). The first indications of a cell-plate are 
shown by the thickening of the spindle fibres near the middle (Fig. 5), 
while in Fig. 6 a delicate cell-plate is shown extending almost completely 
