234 Barrett,— Development and Sexuality of some 
the importance of such conditions seems lessened. These facts concerning 
the nuclei of these forms indicate a relationship between Polyphagus and 
Ancylistes as close as between Polyphagus and Olpidiopsis , both belonging to 
the Chytridiales. The former probably represents an early type of the 
Zygomycetes, while the latter represents a primitive Oomycete. Similar 
types are found among the Ancylistales, as Ancylistes for the Oomycetes and 
Zygochytrium for the Zygomycetes, although the cytology of the latter form 
is not known. Lagenidium also shows a relation to the Zygomycetes, but 
here again nothing is known about its cytology. 
The entire absence of an antheridial tube and the passage of the 
entire contents of the antheridium into the oogonium suggest, according to 
Atkinson (1), ‘ a primitive and generalized condition of sexuality rather than 
a condition of degeneration from forms in which it is more highly specialized.’ 
It would be interesting to know the cytology of the closely related 
genus P seudolpidium^ in which resting spores very similar to those of Olpi - 
diopsis , but without a companion or antheridial cell, are produced. In 
view of the conditions found by Fisch (10) in Reessia and Griggs (14) in 
Monochy triu m , it seems not altogether impossible that in that genus there 
may be a similar fusion of elements that has been overlooked. 
6. Summary. 
1. The zoospores of all three species of Olpidiopsis studied possess two 
cilia of equal length attached at or near the anterior end of the elongated 
body. They have two motile stages separated by a brief period of rest, 
which suggests a primitive type of diplanetism. 
2. The individuality of the zoospore after entrance into the host is 
maintained throughout its development, there being no plasmodium formed. 
Aside from a slight amoeboid movement immediately after entrance, the 
parasite does not undergo any noticeable changes in form. 
3. Segmentation of the sporangial contents has, at least partially, taken 
place before the entrance of the sporangium into a period of rest, when such 
occurs, and is apparently simultaneous throughout. The zoospores on 
escaping contain vacuoles. 
4. True sexuality probably exists, and takes place by the fusion of two 
sexually differentiated individuals and the subsequent passage of the proto- 
plasm of the smaller, male, into the larger, female, cell. This is followed by 
a supposed fusion of nuclei. 
5. Both sexual and asexual reproductive bodies develop rather rapidly 
from a uninucleate to a multinucleate condition. The oospore is likewise 
multinucleate. 
6 . External conditions play a great part in the determination of sex in 
these organisms. This fact adds evidence to the doctrine that sex in many 
plants is determinable by external or nutritive conditions. 
