Cytology of Polyphagus Euglenae. 1 8 1 
The examination of stained specimens shows that the nuclei of the 
fusing gametes have exactly the same structure as those of the ordinary 
vegetative cells. The male nucleus is, however, usually smaller than the 
female, and contains less chromatin. 
The passage of the male nucleus through the pseudopodium is of con- 
siderable interest, but the mechanism by which it is brought about is 
obscure. The delicate pseudopodium is much smaller in the diameter of 
its lumen than the nucleus, and must therefore offer a certain resistance to 
its passage. The force which drives the nucleus along may possibly be 
derived from a combination of the turgescence of the male cell with the 
vacuum caused by the increasing expansion of the young zygote at the end 
of the pseudopodium, or it may be that some attraction is exerted by the 
female cell upon the protoplasm of the male cell. The delicate wall of the 
pseudopodium is probably very elastic, and although I have never seen 
a nucleus during its passage through the pseudopodium, it is clear that the 
wall expands sufficiently to allow the nucleus to pass through it readily. 
There is no evidence that the nucleus has any motive power of its own to 
enable it to force its way along the pseudopodium, and it does not seem 
likely that the delicate wall of the pseudopodium is capable of a rhythmical 
expansion and contraction sufficient to bring it about. 
In the zygote the two sexual nuclei come into contact with each other 
(Fig. 61). Then the smaller male nucleus begins to increase in size, 
probably at the expense of food material in the zygote, and this continues 
until it is almost exactly similar in size to the female nucleus. The two 
nuclei then move apart to opposite sides of the cell (Fig. 62). 
When the zygote is first formed it frequently contains, scattered through 
the cytoplasm, a number of deeply stainable granules, which are probably 
the remains of the dense granular masses derived from the gametes at the 
time of fusion (Figs. 61, 62). Dangeard (’00) has noticed these and called 
them coenospheres. As the zygote develops they gradually disappear, and 
at the same time the oily contents of the cytoplasm increase in quantity to 
form a supply of reserve food material for use at a later stage. 
The two nuclei then undergo considerable changes. Chromatin 
material in the form of amorphous masses or granules is extruded from 
them into the cytoplasm, and they become smaller and lose to some extent 
their capacity for stains (Figs. 63-66). The extruded granules stain very 
deeply in nuclear stains and give a strong reaction for organically combined 
phosphorus. They are obviously of the nature of chromidia, similar to 
those described by Hertwig (’ 07 ) and others in the Protozoa. They form 
conspicuous elements in the zygote at this stage, and become massed 
together into two more or less distinct groups (Fig. 67), one being produced 
by each nucleus. Shortly after their appearance they fuse together into 
a single dense mass in the centre of the zygote (Figs, 68-73). The two 
