177 
Cytology of Polyphagus Euglenae. 
place in the zoosporangium, a large part of this chromatin mass becomes 
extruded into the cytoplasm (Fig. 30), a small portion only being retained 
for the formation of the chromosomes. 
The nucleus is surrounded by a dense granular mass which stains 
deeply in nuclear stains (Figs. 1-5, 54-58). The structure of this mass is 
interesting. It consists of a cytoplasmic network, the meshes of which 
enclose spherical globules of oil (Figs. 55, 57), the knots of the network 
consisting of deeply stainable irregular granules, which give the character- 
istic reaction of chromatin, in that they are deeply stainable in nuclear 
stains, and give a distinct reaction for organically combined phosphorus. 
It is possible that this chromatin-like substance is concerned in the pro- 
duction of the oil. It appears first in the young zoospore at a late stage in 
its formation in the zoosporangium, as a dense stainable mass around the 
nucleus (Figs. 46, 47). It seems to be due to an aggregation of minute 
stainable granules from the cytoplasm, but may also be partly derived 
from the nucleus. Chromatin-like substance is constantly extruded from 
the nuclei at various stages in their development, and notably in the 
sporangia and zygotes. As soon as the zoospore comes to rest and begins 
to germinate, this dense mass becomes gradually filled with globules of oil 
or fatty substance, and is thus transformed into a deeply stainable sponge- 
like granular mass (Figs. 54, 55). During the formation of the zoosporangium 
this deeply stainable mass, together with the oil, passes into it and becomes 
broken up and dissipated in the cytoplasm in the form of minute granules. 
Zoospores. 
The structure ot the zoospore is very simple. At the anterior end, 
immediately below the single cilium, is a yellow or orange-coloured oil-drop, 
and below this the colourless protoplasm with a nucleus (Figs. 21, 48). The 
protoplasm at the posterior end of the spore is granular, and forms a slightly 
flattened mass which is very conspicuous (Fig. 21). Nowakowski regards 
the oil-drop as a nucleus ; Zopf takes a similar view, but states that the 
nucleus owes its strong refractive power to the fact that it contains oil. 
From observations which I have made on stained specimens at various 
stages in their development, the oil-drop is found to be in close contact with 
the nucleus but not inside it (Fig. 48). The zoospores vary very much in 
size. Nowakowski gives their measurements as 6 x 3/x to 13 x 5/x, and I have 
found them varying from 5 x 3 /x to 12x6 [i. Even in the same sporangium 
considerable variation may be found, especially in the sexual sporangia. 
The zoospores of Polyphagus are phototactic, and they are thus enabled 
to make their way to those regions where the host-cells, which are also 
phototactic, may have accumulated. The mechanism by which the direction 
of locomotion is effected by the light is not apparent, but it is significant, 
as I have previously pointed out (’ 99 ), that the orange-coloured oil-drop is 
