128 SAPROLEGNIA Ex'IDEMIC. 



greyish-white flocculent fungoid patches covering the skin 

 of the greater part of the head, body and fins — detached 

 and flaky in places. Entangled amongst the fungus were 

 particles of reddish or orange grit probably added bj' the 

 fish in its attempts to rub off the parasite against the river 

 bank or gravel. On examination the fungus was seen to 

 possess the characters of the genus Saprolegnia, falling 

 into the subgenus Eusaprolegnia {S. ferax group) as 

 defined by Schroeter* and by Hoferf. Though abundant 

 sporangia were present, no mature sexual organs were 

 detected and consequently a sjoecific determination could 

 not be satisfactorily made, though the parasite is most 

 probably S. ferax Nees (or S. thureti de Bary, Avhich 

 ajDparently is a sjaionymj). Huxley gave an account of 

 S. monoica** a very closelj' related form which also affects 

 fish?. 



The gills were invaded, and on examination were 

 seen to be partly denuded of their epithelium and even of 

 ^ome of their more deeply-lying tissues, so that parts of 

 the branchial arches came to jjroject freely. The whole 

 gill apparatus was clogged by the presence of large blood 

 clots and mucus penetrated by the mycelium from which 

 sporangia were developed. Sections of an infected gill 

 and of the skin were made. Ljing above the skin was a 

 covering or feltwork of hyphae which readily became 

 detached during the manipulation, but the rooting hyphae 

 or haustoria could be seen at intervals penetrating into the 



* J. Schroeter. Saprolegniinse in Engler and Prani I's Natuilichen 

 pflanzenfainilien Teil 1, Abt. 1, 1897, pp. 97-8, and fig. 77 B. and C. 



t B. Hofer. Handb. d. Fischkranklu-iten. Stuttgart, 1906, pp. 106-7. 



J F. Guegucn. Les Champignons parasites dc Thomnie et des 

 animaux, Paris, 1904 ; p. 82,_ pi. 6. 



** T. Huxley. Saprolegnia in relation to the salmon disease. Q.J. 

 M.S. 22, 1882 ; Nature 2n, 1882, p. 437. 



Gueguen. I. c, p. 81. 



Schroeter I. c, p. 98. 



§The chief literature regarding Sa])rolegnia is lisltd bj' Schioettr 

 (l. c, p. 93); Gueguen (I. c, pp. 90-2); and De Bary, Vergl. Morphol. 

 n. Biol. d. Pilze. 1884, p. 157. Cytological work on one species of the 

 genus has been published recently by P. Dangeard (Bull. Soc. Mycol. 

 France, 32, 1916, pp. 87-96), an abstract appearing in the J. R. Micr. Soc, 

 1917, (3), p. 323. Various methods of cultivating Saprolegnia ha\e been 

 published, the information being summarised by Gueguen (I. e., p. 79-80) 



