Egg Parasites and their Relatives. 149 



Pythium, Pringshemi. — Infusorioid spores formed at the 

 orifice of the sporangia froni their ejected contents, not sur- 

 rounded by a membrane. Basal membrane neither prolonged 

 into the cavity of the sporangium nor bursting out laterally. 

 Oogonia containing a single resting spore. (Figs. 14 — 16.) 



Aphanomyces, De Bary. — Infusorioid spores formed in a 

 single row in long cylindrical tubes, collected in heads after 

 then discharge, and acquiring a membrane before becoming 

 free. Resting spores single in the Oogonia. Antheridia 

 formed from the swollen tips of lateral branches. (Figs. 17 — 20.) 



The parasite I have more especially seen on fish eggs 

 belongs to the first genus, but as it has produced sporangia 

 only, it is scarcely possible to speak positively as to the species, 

 though I believe it to be referrible to Saprolegnia ferax. 



To make this history more intelligible I will describe one 

 or more species of each genus, in the course of which the 

 technical terms used above will appear more clear. 



The first appearance of Saprolegnia monoica, as indeed also of 

 S. ferax, is that of delicate white or greyish, nearly equal, simple 

 or slightly-branched threads, without any joints, radiating in 

 every direction, and containing a grumous granulated mass. 

 The tips of these threads gradually swell, and after a time a 

 septum is formed at the base, after which the contents are 

 collected into little pellets, each of which, at length, is separated 

 from the rest, and becomes an ovate spore (Fig. 3), which 

 escapes by a little aperture at the tip, and is furnished with one 

 or two delicate thread-like appendages, by means of which it is 

 able to move about like an infusorial animal with great rapidity. 

 After a short time motion ceases, and the spore germinates and 

 produces a new plant. (Fig. 4.) 



After the sporangium is exhausted the septum at the base 

 becomes convex, pushes forward (Fig. 2) into the vacant cavity, 

 which it more or less completely fills, and produces another 

 crop of spores, sometimes projecting through the aperture of 

 that- which was first formed. This process is repeated a third 

 or even a fourth time till the powers of vegetation are 

 exhausted. 



Now, however, a second form of fruit (Fig. 5) appears. A 

 form which has been called an Oogonium, because it produces 

 spores which are quiescent and dormant for a time like eggs, 

 and not furnished with motile appendages. Lateral branches 

 are given off for their production, which terminate in large 

 globose sacs, which, like the sporangia, are not at first separated 

 by any septum. One, however, is at length formed, and the 

 membrane becomes pierced with numerous apertures. Mean- 

 while other branches (as in S. monoica) spring up in their 

 neighbourhood, the tips of which swell, and at length become 



