Wilson. — Spermatogenesis in the Bryophyta . 423 
February, and ripe spermatozoids are produced from about the middle of 
March to the end of May. Material preserved during the middle and later 
parts of this period generally shows all stages of development. In the 
young antheridium the spermatogenic cells can easily be distinguished 
from the wall-cells by their dense cytoplasm and large conspicuous nuclei. 
In the wall-cells the nucleus is small and is almost hidden by the large 
chloroplasts with which the cell is closely packed. The spermatogenic 
cells are generally cubical in form and are regularly arranged, but the 
shape and arrangement are not so constant as in the antheridia of many of 
the Hepaticae, the cells being occasionally oblong or polygonal. 
In their structure the cells closely resemble those previously described 
(74) in the archesporium (PI. XXXVII, Fig. 1). The protoplasm is very 
finely alveolar, without vacuoles, and no deeply staining granules are 
present. The nucleus is large in proportion to the cell, and possesses a 
large deeply staining nucleolus. The nuclear network is fine and closely 
resembles the cytoplasm in structure, no chromatin being present in it 
during the resting condition. 
The earlier divisions in the antheridium closely resemble those occur- 
ring in the archesporium. At the commencement of the prophase the 
nucleus becomes more granular and chromatin appears in the network. No 
body is cut off from the nucleolus, and no sign of centrosomes was found at 
this or at later stages in the division. The spireme stage is evidently of 
short duration, for few cells were discovered in this condition. At the 
metaphase six chromosomes appear on the equatorial plate (Fig. 2). Each 
is slender, elongated, and hooked, the short arm usually lying parallel with 
the equator of the spindle. In consequence of the statements made by 
J. and W. Docters van Leeuwen-Reijnvaan concerning the difference in 
size of the chromosomes of Poly trichum (41) and Mniutn (42), a careful 
examination was made both in side and in polar views, but no definite varia- 
tion in size was discovered — the chromosomes are of approximately equal 
length. In polar view (Fig. 3) each chromosome is seen as a sharply 
bent rod with the convex side towards the centre. Both Arens (2) and 
J. and W. Docters van Leeuwen-Reijnvaan (42) have given the chromosome 
number in Mnium as eight, but the former subsequently corrected this to 
six (3). Although the cell is small, there is no doubt as to the number 
present. This number has also been previously described in the meiosis. 
The spindle at this stage is ill-defined, but the fibres can be more clearly 
seen at the anaphase. No centrosomes are found at the poles. The 
absence of centrosomes can be stated with considerable certainty, since the 
cytoplasm is of very regular structure and there is a complete lack of 
deeply staining granules of any kind. 
The subsequent divisions in the antheridium agree in their general 
characters with the description just given, and on this account considerable 
F f 2 
