324 SPENCER WAI.POLE AND T. H. HUXLEY. 



which accompanied the epidemic disease affecting roach, 

 dace, gudgeon, small pike, and perch, at Ightham in Kent, of 

 which a very full and interesting account is given hy Mr. 

 Stirling,^ is to be referred to Saprolegnia feraz. Here, 

 however, ulcerative destruction of the skin does not appear 

 to have occurred, and the mortality is said to have arisen 

 from suffocation, the fungus obstructing the respiratory 

 passages. 



Pike kept in aquaria not unfrequently become covered 

 with a fungus. The fish do not appear to be inconvenienced, 

 and the fungus is very easily washed off. In a case of this 

 kind, which we recently examined, the fungus was a S'ajjro- 

 legnia, the mycelium and the zoosporangia of which were 

 altogether indistinguishable from those of the salmon fungus. 

 Moreover, the hyphse burrowed in the epidermis and distorted 

 the cells with which they came in contact in just the fashion 

 described below. As it was not desirable to kill the fish, 

 it was impossible to determine whether the derma was 

 penetrated or not ; but the absence of sores and the ease 

 with which large flakes of epidermis, in which the Sapro- 

 legnia was rooted, could be detached, lead to the conclusion 

 that the Saprolegnia had not penetrated beyond the epi- 

 dermis. The zoosporangia of the Saprolegnia taken from the 

 fish emitted actively locomotive zoospores, but no oosporangia 

 could be detected. 



Dead flies infected with this Saprolegnia on the 18ih of 

 March, 1882, yielded an abundant growth, quite similar to 

 that obtained in the same way from the salmon Saprolegnia ; 

 and on the 24th, that is, in six days, the characteristic 

 oosporangia and antheridia of Saprolegnia ferax [monoica) 

 made their appearance. 



It appears, therefore, that Saprolegnia ferax is capable of 

 attacking a great variety of fishes during life, but that the 

 concomitant pathological phenomena differ in different fishes. 

 Mr. Stirling's experiments on the transmissibility of the 

 salmon fungus to other fish yielded only negative results. 

 Diseased salmon skin was put into a vessel containing min- 

 nows, which nibbled the skin, and were none the worse. 

 Experiments of this rough-and-ready sort, however, really 

 prove nothing ; and a great deal of light will assuredly be 

 thrown upon the whole question of the salmon disease by 

 carefully conducted experimental investigations. 



At the present moment, we possess evidence that at least 

 three distinct affections of the skin of fresh-water fishes have 



^ " Additional Observations on Fungus Disease of Salmon and other 

 Fish," • Proceedings of the Uojal Society of Edinburgh,' x, 1879. 



