280 Trow. — Observations on the Biology and 
dense central mass as the egg, and the clear peripheral layer 
as the periplasm. The central mass is in continuous move- 
ment, but tends to round itself off more and more, though it 
never acquires a smooth outline like that of the eggs of the 
Saprolegniaceae. Moreover the delicate peripheral layer com- 
pletely disappears as represented in Fig. 4 g 3 so that if we 
accepted the current view as to the significance of the central 
mass, we should have to admit that the periplasm disappears 
during the differentiation of the egg. The warted appearance 
of the central mass is very characteristic of this stage, and is 
apparently due to an accumulation of reserve globules. The 
study of sections proves what the examination of the living 
material leads one to suspect, that the central mass includes 
both egg and periplasm, and that the egg is completely 
masked by a dense mantle of periplasm containing globules 
of reserve material. 
Turning our attention to the antheridium, we note that its 
growth is rapid, and that after a time two or three granular 
aggregations make their appearance in it. These may be 
nuclei, but it was impossible to furnish proof of their real 
nature. As the central mass begins to form in the oogonium 
(see Fig. 4 e), a fertilization-tube becomes apparent, connecting 
the central mass with the antheridium. This gradual dis- 
closure of the fertilization- tube has been generally interpreted 
apparently as its growth . There can be little doubt that it 
was formed before the differentiation of the oogonial contents 
began, as I have never been able to get a view of its apex, 
and have thus never been able to trace its growth. Different 
species of Pythium may behave differently in this respect. 
Certainly De Bary’s figure of Pythium gracile suggests that 
such is the case, and the point thus deserves further investiga- 
tion in other species. 
Fertilization. The question of fertilization is a curious 
one. It seems generally admitted that the process of fertili- 
zation can easily be followed in this genus. Authors, how- 
ever, apparently mean by this that they can trace a slow 
migration of the protoplasm down the fertilization-tube. 
