282 Allen . — The Spermatogenesis of Poly trichum juniperinum. 
or vesicle, whose form is that of the space enclosed in one of the definite 
envelopes of a somewhat earlier period (Fig. 50) ; between these vesicles is 
an orange-stained substance of variable density. The antheridium from 
which Fig. 54 was made shows no such distinction between vesicular and 
intervesicular materials ; and the substance in which the antherozoids lie 
shows no stain, excepting that at places where it abuts upon a perfectly 
clear space it is seen by contrast to have a faint tinge. These two very 
different conditions may be seen in antheridia lying side by side in the 
same section, so that it can hardly be due to differences in the exposure 
to stains ; Figs. 54 and 55 were drawn from different sections (in the 
same preparation) of antheridia from the same head. It is possible that 
these differences indicate different stages in the development of the an- 
theridium; but I find nothing to support this notion, and consider it 
more likely that they represent variations in the conditions within different 
antheridia. 
As the antheridium approaches maturity, there is a considerable 
shrinkage in the mass of its contents, including the androcytes (or an- 
therozoids) and the substances in which they are embedded. This 
shrinkage is observable both in fixed and in living antheridia ; the con- 
tents are contracted, usually towards one side, leaving a large part of the 
cavity of the antheridium apparently empty. This contraction is doubt- 
less due largely or entirely to the fact that the mature antherozoid is 
much smaller than the androcyte from which it has been formed, most 
of the cytoplasm of the latter having disappeared and the antherozoid 
having taken the form of a flattened coil. 
When the opening of a mature antheridium in a drop of water is 
observed under the microscope, each antherozoid is seen to be enclosed in 
a sharply outlined drop of clear liquid which is embedded in turn in a denser 
substance. It is this appearance that has led various observers to describe 
the antherozoid as enclosed in the wall, or the remains of the wall, of the 
‘ mother-cell ’. That there is nothing of the nature of a wall is plain from 
the history already outlined, as well as from the fact that the substances 
surrounding the antherozoids gradually dissolve in water. For some time 
the antherozoids can be observed in rapid movement, each within its own 
vesicle. As the intervesicular substance is gradually dissolved, the vesicles 
become separated from one another ; but the tenacity of the membrane or 
layer immediately surrounding each vesicle is such that, even though the 
mass escaping from an antheridium be left in water for as long as two hours, 
only an occasional antherozoid escapes from its vesicle. Figs. 56-9 
represent antherozoids which were fixed and stained after being set free from 
the antheridium. Those shown in Figs. 56 and 57 were still enclosed in 
their vesicles when fixed. It is noteworthy that the outline of the vesicle 
is quite invisible in such a preparation, and that the intervesicular substance 
