248 Campbell . — On the development 
arises here, at any rate, not by a further division of the central 
cell, but by division of the primary canal-cell. The wall 
dividing the two canal-cells is so high up, and so much shorter 
than the wall by which the primary canal-cell was separated 
from the central cell, that it is hard to see how such changes 
of position could be otherwise accounted for. 
The divisions in the female prothallium are usually com- 
pleted in from forty to forty-five hours from the time the spores 
are sown, and shortly thereafter the archegonium opens and is 
ready for fecundation. Owing to the opacity of the covering 
membranes, the only part of the archegonium that can be seen 
in the living prothallium is the upper part of the neck. The 
cells of this, as in other Pteridophytes, become much distended 
with water and diverge widely when the neck opens, and at 
the same time, as has been so often observed in other Arche- 
goniates, the contents of the disintegrated canal-cells are forced 
out of the opening. 
Fecundation takes place very soon after the archegonium 
opens, the spermatozoids, as already mentioned, collecting 
in great numbers about the open archegonium. The opacity 
of the spore-membranes makes it impossible to follow the 
spermatozoid to the central cell, but this probably takes place 
very quickly owing to the shortness of the neck. In nearly 
every case where the spores were placed in alcohol imme- 
diately after it was supposed that fecundation had been 
effected, the lower neck-cells had already begun to assume the 
dark-brown line indicative of the fact. In these cases the two 
nuclei could generally be demonstrated in the germ-cell. 
The oosphere becomes almost at once surrounded by a 
membrane which prevents the further penetration of sperma- 
tozoids. As soon as the spermatozoid enters the germ-cell it 
appears to go through a similar series of changes, only in 
reverse order, to those which the nucleus of the sperm-cell 
undergoes in forming the spermatozoid. In the earliest stages 
observed, the elongated, more or less curved form of the 
spermatozoid was still indicated, but the body was less homo- 
geneous than in the free spermatozoid. The body was also 
