Species of Olpidiopsis, (Cornu) Fischer, 233 
sexual relation is found in the new genus and species Zygorhizidium Willei 
described by Loewenthal (17). 
The one species, aside from that of Monochytrium , that is well known 
from a cytological point of view, is Polyphagus Euglenae, Now. Nowakow- 
ski described the external phenomenon of the union of the two individuals, 
but the internal behaviour relating to fertilization has until recent years 
remained unknown. The cytology of the form was first worked out by 
Wager (25). According to him the unicellular elements are uninucleate. 
After the fusion of the two protoplasms there ensues a period of rest, and it 
is not until the time of germination of the zygote that the sex nuclei fuse. 
Dangeard (9) took up the study of the same organism and published 
a long memoir on it. He confirmed in general the results of Wager. He 
believes that copulation can take place with the male element before it has 
attained its complete development. This would appear to be another proof 
of his general theory of sexuality. According to this theory, living forms 
primitively asexual have become sexual on account of their resistance to 
unfavourable conditions where they live. In particular, the exhaustion of 
nutritive material brought about a sort of starvation which induced the 
appearance of sexual attraction. 
The similarity of the mode of development and nuclear behaviour of 
the sexual elements of Olpidiopsis species, together with the relation of 
internal conditions to the development of the gametes, point strongly to the 
belief that they are morphologically equivalent to the sporangia. Many of 
the sporangial characters are retained by the male cells or antheridia up to 
the time of fertilization, while more marked differential changes in the 
oogonial forming individuals take place much earlier. 
There appears to be no definite or proper time for the transference of 
the male protoplasm into the oogonium, at least so far as the behaviour of 
the nuclei is concerned. In other words, fusion of the sex protoplasm may 
take place before the maturity of one or both cells. 
These characters, it seems, point to a primitive condition of the sexual 
stage. This view would, according to some students, be strengthened by the 
coenogametic nature of the sex individuals and the multinucleate character 
of the resulting oospore. This condition, however, is not confined to the 
lower forms. A similar condition was described by Stevens (24) for Cysto - 
pus Bliti in a genus showing what appears to be a sequence of species ranging, 
so far as numbers of fusion nuclei present in the oospore are concerned, from 
Cystopus Bliti to Cystopus candidus where only a single nucleus is present. 
Such a sequence occurring among closely allied species seems to indicate 
the gradual change from a primitive form to the more usual condition when 
only one nucleus is present. But when one considers that the sex cells of 
Polyphagus Englenae are uninucleate, and the sex cells and resulting oospores 
of Olpidiopsis and Ancylistes Closterii, Pfit. (Dangeard, 7), are multinucleate, 
