of Marattia Douglasii , Baker . 5 
archegonia, at least, seem to give a possible clue to the origin 
of the sexual organs of the Pteridophytes. 
The Antheridium. 
The general structure of the antheridium and its divisions 
have been so completely described and figured by Jonkman 
that they will be passed over very briefly here. The 
antheridium arises from a single superficial cell which first 
divides into an inner cell, the mother-cell of the sperm-cells, 
and an outer cover-cell. This latter divides by several curved 
vertical walls which intersect, and the last wall cuts off 
a small triangular cell (Fig. 7, 0), which is thrown off when 
the antheridium opens and allows the sperm-cells to escape. 
The inner cell, by repeated divisions, gives rise to a large 
number of polyhedral cells, the sperm-cells. Before these are 
completed, however, cells are cut off from the adjacent cells of 
the prothallium, completely enclosing the mass of sperm-cells 
(Figs. 7-10). In microtome-sections of material stained with 
alum-cochineal, the transformation of the nucleus of the 
sperm-cell into the body of the spermatozoid is easily 
followed. The nucleus of the sperm-cell, at the time when 
the division is complete, has the appearance of an ordinary 
resting nucleus, but no nucleolus is visible. The first sign of 
the formation of the spermatozoid that could be seen, was an 
indentation upon one side followed by a rapid flattening and 
growth of the whole nucleus. The cytoplasmic prominence, 
which according to Strasburger 1 is the first indication of the 
formation of the spermatozoid, could not be detected in 
material stained with alum-cochineal, and although in some- 
what later stages (see Fig. 11, a) a slight elongation of the 
forward end of the spermatozoid was sometimes noticed, it 
was vague and its limits uncertain. The main part of the 
body stains strongly with alum-cochineal, and for some time 
shows unmistakably the nuclear structure, and is sharply 
differentiated against the colourless cytoplasm. In the later 
1 Strasburger, Histologische Beitr'age, Heft IV, p. 116. 
