of the Fishery Board for Scotland. 



375 



believed to remain at rest for a very long time, even months before 

 germinating. 



The oosporangium may, however, by immediate rupture set free the 

 oospores, which may at once germinate without passing through a resting 

 period. When an oosporangium is ripe it may discharge its within con- 

 tained brood, or may drop off and fall to the bottom while still containing 

 the oospores, just as we find with many of our fruits ; the seeds may be 

 found scattered on the ground or the capsule may be found with the seeds 

 still contained within them. The capsule, therefore, of the oosporangium 

 has no function after the oospores have attained their maturity. When, 

 however, their period of rest comes to an end, and this may perhaps be 

 decided by the onset of conditions favourable not merely for their germina- 

 tion but also for successful aftergrowth, they may proceed in one or other 

 of the following ways : — 



(1.) The ripe oospores may have their contained protoplasm by a process 

 of division formed into a number of zoospores, which by subsequent 

 rupture are set free. 



(2.) The whole oospore may proceed in somewhat the same manner as 

 an ordinary spore, sending out a hypha of mycelium, which later may 

 give rise at its summit to the formation of a sporangium, but, in this case, 

 it is not necessary for the oospore to become attached to a nutrient soil as 

 is the case with ordinary spores. Here then the oospore is somewhat 

 analogous to those seeds of higher plants, which contain a store of suitable 

 nourishment, to meet the requirements of the young growing embryo. 



(3.) The oospore may proceed in exactly the same way as an ordinary 

 spore, becoming attached to a dead insect or other material, into which 

 it sends a hypha which then branches into an ordinary mycelium in the 

 usual way. 



While, therefore, there is here indicated, as far as we at present know, 

 the whole series of events possible in the Saprolegnia as a genus, we must 

 note that in certain of the species variations may occur, but it is very 

 difficult to define the species accurately, for reasons which will after- 

 wards appear. 



The definition of the species of Saprolegnia, depends upon the recogni- 

 tion of certain characteristics, as for instance, the forms assumed by the 

 sporangia, the forms and manner of emission of the ripe spores, and the 

 presence of antheridia. 



In certain forms the sporangium approaches in shape more nearly to the 

 spherical, and there may be instead of a single terminal one a succession 

 of such bodies, assuming a somewhat necklace-like arrangement. Such 

 a peculiarity obtains in S. torulosa, and as such has been described as a 

 different species from the more common variety of Saprolegnia known as 

 S.ferax. However, Pringsheim and De Bary both consider that not only 

 this species but several others, as S. thureti and S. monoica are but 

 varieties of the S. ferax. 



It seems to be pretty certain that oosporangia are very rarely found 

 in salmon afflicted with the fungus, as Mr Stirling speaks of having 

 only observed it on four occasions during the whole course of his investi- 

 gations, and Mr Huxley, in his report for the year 1881, states that not a 

 single one was seen in any of the fish examined during the course of the 

 previous four months. Up to the present moment I have only had an 

 opportunity of examining nine salmon, specially for this purpose, and in 

 none of these did I find any oosporangia, although I made a very careful 

 examination in each case. S. ferax is supposed by many to be identical 

 with the fungus known as Achy la prolifera affecting flies, and Pringsheim 

 considered Achyla so plentiful that, if one wishes a cultivation of it, he 



