Inter-Relationships of Protista and Primitive Fungi 279 
which it arose, lies freely within the cytoplasm of the host-cell, and 
the zoospores (or zoogametes, as the case may be) escape by means 
of a tube, or several tubes in some cases (e.g. Pleotrachelus, Fig. 6, D) 
which are protruded by the germinating sporangium and pierce the 
wall of the host-cell. In Sphcerita, however, described incompletely 
by Dangeard (1886, 1887) the sporangium opens by decay of its 
wall, the zoospores being set free after death of the host Rhizopod 
or Flagellate : in Pleolpidiutn the sporangium fills the host-cell so 
that its membrane comes into contact with and finally fuses with 
the cell-wall and the zoospores escape through a pore formed by 
absorption of the two walls at the point of contact; and in 
Eurychasma , according to Loewenthal (1904) and Magnus (1905), 
the zoosporangium swells so as finally to burst through the wall of 
the host-cell, its coat opening to liberate the zoospores by means of 
one or more slits or pores—Petersen (1905) makes this genus the 
type of a new family, Eurychasmaceae, but this appears unnecessary. 
In Olpidium vicice, Kusano (1912) observed conjugation of 
free-swimming zoospores (isogametes), and found that while both 
conjugated and unconjugated swarmers may infect the host, the 
former give rise to resting cysts and the latter to zoosporangia; 
on penetrating the host the young parasite enters the cell and 
comes to rest near the nucleus, being carried round by the rotation 
of the host cytoplasm and, though naked until nearly mature, not 
showing amoeboid movement as in Reessia and Monochytrium. 
The nuclei of the zoosporangium divide during the earlier (vegetative 
or growth) stages by amitosis, as described by Griggs in Mono¬ 
chytrium , but in the later (reproductive or spore-forming) stages by 
mitosis. In Olpidium salicornice (Fig. 6, A), Nemec (1911) states 
that although all the naked and at first amoeboid parasites appear 
alike, some give rise directly by repeated nuclear division to thin- 
walled zoosporangia, while others conjugate in pairs within the 
host-cell, as in Monochytrium but with fusion of nuclei as well as 
cytoplasm, to form zygotes which produce the resting sporangia. 
Before considering some other forms which are clearly related 
to Olpidium and its allies, it may be noted that Schroter’s family 
Oochytriaceae is an unnatural one, and that the three genera 
constituting it ( Diplophysa , Polyphagus and Urophlyctis) should be 
distributed among other families of Chytridiales. The genus 
Olpidiopsis was founded by Cornu in 1872 for a number of forms 
which differed from Olpidium mainly in the resting sporangium 
having a spiny instead of a smooth coat, and in having attached to 
each sporangium an empty smaller cell which he suspected was an 
antheridium. In 1883 Zopf described a new species, 0. schenckiana , 
in which the sexual process was practically proved—the sexual 
plant arose as a single mass of protoplasm which later put out a 
process to form the companion cell or antheridium, this becoming 
completely emptied, though no actual pore was observed between 
it and the large remaining portion (oogonium) which developed 
into the resting-spore (or sporangium). Next year Fisch described 
a new form, Pleocystidium parasiticum, resembling O. schenckiana 
and like it parasitic on Spirogyra, but differing in that the sexual 
spores arose from two or more associated protoplasmic masses 
representing separate individuals; one of these became what he 
called the central cell (oogonium) and the others the companion 
