THE GAMETOPHYTE OF PSJLOTUM. 
89 
which are set free when mature by the swelling of the contents and the breaking 
down of one or more of the central cells of the wall. The wall in section is seen to 
consist of from six to eight cells, the base of the antheridium being supported upon 
two or four large cells. The spermatozoids can be seen within a mature antheridium 
to be spirally wound. When set free they uncoil somewhat, and are propelled by 
numerous cilia. One portion of the spermatozoid, placed externally along the greater 
portion of the spire, stains much more readily than the rest. The antheridia are 
found at a very early stage in the development of the prothallus. They may 
develop upon any part of the cylindrical body. When young they arise immediately 
behind the growing point, and appear as small, white, glistening knobs ; when older 
they turn brown (see figs. 26, 27, and 28). 
7. The Archegonium. 
In the archegonium the oosphere lies in a sunken hexagonal venter, the walls 
of which are brown and much thickened. The median cell -wall immediately below 
the venter is much thickened also. The projecting neck of the archegonium consists 
of four tiers of four cells enclosing a ventral canal cell and apparently two canal 
cells. The three upper tiers of canal cells break off very easily when cleaning a 
prothallus (see figs. 22 and 23). 
The breaking off of the three upper tiers of canal cells is rendered the more liable 
to occur in older archegonia because the product of the breaking down of the canal 
cells becomes hard and brittle, and in many preparations will be found projecting as 
a small spike between the four canal cells that are left. 
The four basal canal cells are slightly sunk in the prothallus, and their walls, 
except those adjoining the prothallium, are somewhat thickened. The ragged edge 
left where the superimposed tier of cells has been broken off may be frequently 
observed. 
On account of the lowest tier of four canal cells only remaining attached to the 
mounted prothallus, and the dark brown colour of the venter walls, the archegonia 
appear in surface view as dark brown spots surrounded by four raised cells arranged 
symmetrically in the form of a rosette, the outer wall of each cell being sharply 
curved (fig. 25). 
The oosphere, which completely fills the venter, contains a large nucleus which 
itself often contains from two to three bodies, which stain deeply. Similar deeply 
staining bodies are sometimes found in the cytoplasm. These deeply staining bodies 
may be sections of spermatozoids ; but as no longitudinal section of a spermatozoid 
that would place the matter beyond doubt has been obtained, the suggestion must 
be regarded as purely tentative (fig. 24). 
The archegonia usually occur upon the older parts of the prothallium, and may 
arise upon any part of its circumference. They are interspersed among the antheridia, 
and often occur more or less in groups. 
