196 Wager . — The Life-history and 
surrounded by a deeply stained chromidial mass, which extends also around 
the oil-drop to the point of attachment of the flagellum. It is suggested 
that the yellow-coloured oil-drop may be functional in connexion with the 
phototaxis of the zoospores. 
4. The nucleus of the vegetative cell contains a large chromatin 
nucleolus, which is frequently arc-shaped and is in close contact with 
a lightly stainable nucleoplasm. The nucleus is surrounded on all sides 
by a deeply stained mass of chromidia. 
5. The zygotes are formed by the fusion of uninucleate gametes, which 
are equivalent to vegetative cells. They are placed in contact with each 
other by means of a copulating tube which is put out from the smaller 
or male cell and comes into contact with the larger, female cell. The apex 
of the copulating tube swells up and becomes the zygote. The contents 
of the male tube first pass into it, then the contents of the female cell. 
6. The two sexual nuclei in the young zygote are at first unequal 
in size, but the smaller male nucleus grows, probably at the expense of 
nourishment brought in from the female cell, until it becomes equal in size 
to the female nucleus. Large quantities of chromatin are then extruded 
from the two nuclei to form two masses of chromidia which fuse and form 
a large granular mass for which the term ‘ chromidiosphere ’ (or ‘ chromidio- 
centrum ’) is suggested. The significance of the chromidia and the chromidial 
fusion is briefly discussed. 
7. The germination of the zygote has been followed in detail both in 
living and stained specimens. It was observed to take place in November, 
five months after the formation of the zygotes. The outer spiny coat 
is ruptured, and a delicate protuberance appears which develops into 
a zoosporangium similar to the ordinary asexual sporangium, except that 
it is usually much smaller. The two sexual nuclei do not fuse until after 
their entry into the sporangium. 
8. Nuclear division takes place only in the sporangia, never in the 
vegetative cells, cysts, or zygotes. The process has been followed in the 
asexual sporangia. The spindle is internal ; the nuclear wall breaks down 
first at the poles, where kinoplasmic substance with radiating striae appear. 
The prophases and anaphases of division appear to be those of normal 
mitosis, but, compared with the large amount of chromatin in the resting 
nucleus, the chromosomes are small. 
9. With the exception of Olpidiopsis and Olpidium , the cytology of the 
Chytridiaceae is not very completely known, and there are many accounts 
of curious abnormal nuclear phenomena, especially in Synchytrinm , which 
require elucidation in view of the perfectly normal mitosis in Polyphagus 
and Olpidiopsis. 
3 0. Polyphagus shows relationships with various other genera of the 
Chytridiaceae, leading on the one hand to the Oomycetes and on the other 
