of Edinburgh, Session 1878-79. 
248 
as every kind of fish, irrespective of condition, appears to be a 
proper nidus for the propagation of the Saprolegnia ferax when a 
living spore from that fungus attaches itself to it. While engaged 
during the spring and summer in the microscopic examination of the 
Saprolegnia ferax , I observed that as the season advanced many of 
the patches of fungus seated upon the fish were barren, consisting of 
spear-shaped filaments only, having no zoosporangia at their apex, 
and consequently they produced no zoospores ; the filaments were 
long and very thin, and almost void of protoplasmic contents, indi- 
cating that the plant was losing its force and in a state of decay. 
The Saprolegnia ferax , in all probability, is always present in 
our rivers in more or less active condition. It is believed that this 
fungus has two modes of reproduction, namely, by oospores and by 
zoospores. The oospores are few in number, and may be looked 
upon as ova, and they require sexual impregnation. They are 
called resting spores, from a belief that they remain dormant in 
the water for an indefinite period, which may continue for many 
years ; and during this phase of their life they may germinate in 
limited numbers, providing only for the continued existence of the 
species. While in this state of abeyance there is no plague of 
fungus, from the ova only producing neutral or barren plants, which 
bear no fruit or seed. After a period, of longer or shorter duration, 
a season, or a series of seasons, may follow, during which an un- 
known influence arises, which acts upon the resting spores, by 
which they are stimulated to great reproductive energy ; and the 
plants they produce being fruitful, the asexual mode of reproduction 
commences. 
The zoospores are produced in podlike cases called zoosporangia, 
which are situated at the apex of the filaments, and may be looked 
upon as fruit or seed. They are the ciliated spores, and are the 
media by which the fungus is communicated to the fish. The 
zoospores are produced in great numbers, each zoosporangium con- 
taining from 100 to 150 of them. The oospores or ova are produced 
in a globular sac, which forms at the root ends of the filaments, or 
upon the roots themselves. Those sacs are called oogonia, and each 
sac contains a few oospores or ova, three or four, to nine, being the 
numbers I have observed in the four instances in which I have seen 
them, in the whole course of my investigations. 
