444 Wilson. — Spermatogenesis in the Bryophyta. 
nucleus during the subsequent extension. The thread, which is constantly 
found on the outer contour of the nucleus, must consequently undergo an 
equal increase in length. 
The elongation as shown by Guignard (26 a) and Campbell (16) takes 
place in a plane parallel to that of the wall which divided the mother-cell, 
and on this account can be most easily observed in those cells so placed as 
to appear circular in optical section. In this respect Pellia agrees with 
Monoclea Forsteri , in which Johnson (37) states that the axis of the spiral 
formed by the spermatozoid is perpendicular to the plane dividing the 
mother-cell. A comparison of the Cycads and Ginkgo is also of interest in 
this connexion. In these plants, as far as they have been investigated, the 
axis of the spermatozoid is always perpendicular to the wall dividing the 
mother-cells, and here again there is complete agreement with Pellia in 
this respect. On the other hand, in Ikeno’s account of Marchantia (32), 
although no statement is made as to the orientation of the plane of elonga- 
tion, judging from the figures given, this plane is at right angles to that of 
the divisional plane of the mother-cell. An examination of the drawings of 
Fossombronia given by Humphrey (30) leads apparently to the conclusion 
that this plant resembles Marchantia in this respect. 
The elongation of the nucleus proceeds until the ends come almost in 
contact (PI. XXXVIII, Fig. 8o), and then further extension goes on in 
a spiral above or below the level of the first coil (Fig. 8i). This increase 
in length is accompanied by contraction of the substance of the nucleus 
and consequent decrease in width. The cytoplasm meanwhile diminishes 
in amount, and is found in the portion of the spermatid enclosed by the first 
coil. When the spermatozoid has reached its full length it consists of a spiral 
of about three turns. 
No observations have been made on the free swimming spermatozoid, 
and during the various stages of development no traces of the cilia were 
found, although special staining methods were employed to render them 
visible. Consequently no statement can be made as to their exact place of 
attachment, although they may be presumed to arise from the blepharo- 
plast. 
Discussion and Conclusions. 
In the above description it has been shown that the mitoses which take 
place during the development of the antheridia of Mnium hornum and 
A trichum undulatum are of the normal type. The final division of the 
spermatogenic cells does not differ essentially from those mitoses which 
immediately precede it, but in fact resembles them so closely that there is 
considerable difficulty in distinguishing it. It is clear that no reduction in 
the number of chromosomes takes place in the antheridia of these plants. 
It may also be concluded with considerable certainty that no reducing 
