440 Wilson. — Spermatogenesis in the Bryophyta . 
The nucleus of the spermatid is centrally placed, and is very large in 
comparison with the size of the cell, almost extending across its whole 
width. It is oval in shape and contains a number of irregularly shaped 
masses of chromatin usually massed towards the centre, while no definite 
nucleolus is present The cytoplasm is very regular in structure and contains 
no deeply staining granules. The blepharoplast soon appears as a small 
intensely staining spherical body. It can be first distinguished at about the 
middle of the curved wall of the spermatid lying in the protoplasm midway 
between the nucleus and the periphery of the cell (PI. XXXVIII, Fig. 6 9). 
The origin of the blepharoplast was not determined, but the position in 
which it was first observed is suggestive. This spot was occupied by the 
pole of the spindle in the division of the mother-cell, and it is the place at 
which a centrosome, if present, would probably be found. Although a com- 
plete investigation has not been made, it has been shown that there is con- 
siderable evidence for the presence of a centrosome at the final division. 
It is difficult to avoid the inference that this body persists as the blepharo- 
plast, or, at any rate, is genetically connected with it. The latter is larger 
and stains more deeply than the bodies seen at the spindle poles, but this 
increase of size and of staining capacity in the developing spermatid is not 
surprising. It must, however, be borne in mind that the appearance of the 
blepharoplast in this position does not exclude the possibility of its nuclear 
origin. It is hoped to deal with this matter fully in a subsequent paper. 
The blepharoplast now approaches the plane surface, always remaining 
during its passage a short distance from the curved wall (Fig. 70). As seen 
in side view it frequently passes towards one end of the spermatid, but this 
is not constantly the case, as it may finally occupy any position along the 
junction of the curved and the plane surfaces, and hence appear at any 
spot on the flat wall. The blepharoplasts are often similarly orientated in 
each spermatid of the pair, and in this case may be found in side view 
occupying the correspondingly adjacent angles (Fig. 73). On the other 
hand, they may be seen in the widely separated angles (Fig. 72). The 
nucleus, up to this time, has retained its central position in the cell, but 
now passes towards the periphery and is finally discovered in contact with 
the membrane at a short distance from the blepharoplast (Fig. 74). 
A thread of stainable substance is now formed in connexion with the 
blepharoplast, extending over the inner contour of the cell membrane and 
passing along the edge of the plane surface. It soon reaches the area in 
contact with the nucleus and passes beyond it, terminating at the opposite 
side of the cell (Fig. 77). At present it must be left an open question 
whether the thread is due to an extension of the blepharoplast substance or 
whether it is produced by a differentiation of the cytoplasmic membrane in 
connexion with the blepharoplast. 
At this stage it is necessary to consider in detail the appearances pro- 
