432 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



but sometimes the granules are sufficiently numerous to render it opaque ; 

 and tlien it looks white by reflected light. Sometimes the filauients are 

 simple as far as they can be traced; sometimes, on the other hand, they 

 are much branched; but they never exhibit any trans\'erse partitions, 

 the cavity of each filament being continuous throughout. Wherever 

 the free end of a filament is to be seen it is rounded, closed, and often 

 no larger than the rest; or the filament may taper to its extremity. 

 But the free ends of a greater or less number of the filaments are slightly 

 enlarged, so as to be club-shaped, or they may be pyriform, or even 

 almost spheroidal, and the layer of protoplasm which they contain is 

 very thick. The cavities of some of these eJilarged ends are shut off by 

 a transverse partition from the rest of the filament, thus giving rise to 

 a closed case. In others the protoplasm is broken uj) into a number, 

 greater or less, according to the size of the enlargement, of equal-sized 

 spherical masses, each rather less than ^oVo <^f ^u i"ch in diameter, 

 which lie separae, but closely packed in the interior of the case, like 

 shot in a cartridge. (Fig. I, p. 433.) In others the case is seen to be 

 open at the end, and a portion or the whole of the "shot" have passed 

 out. In yet others, again, a full unopened case is seen to lie inside an 

 empty one. 



The papyraceous mass is, in fact, what is known as the mycelium of 

 a fungus. It answers exactly to the similar, wet-paper like, crust which 

 is formed by the common fungus, PeniciUiDii glaucuvi (usually known as 

 " blue mould "), on the surface of a i)ot of jam. The filaments are the 

 stems of the fungus, and are technically known as hyphcc. The enlarged 

 ends of the hypha3, which are converted into the " cases," are the 

 sporangia^ or fruits of the fungus, and they are termed zoGsporarujia, 

 inasmuch as the spheroidal bodies or spores, under certain circum- 

 stances, are actively locomotive, after the fashion of many animalcules, 

 and are therefore termed zoospores. It is a peculiarity of this i)articular 

 fungus that, when a zoosporangium has emptied itself, the hypha on 

 "which it is supported begins to grow afresh, sends a prolongation 

 through the centre of the empty sporangium, and dilates into a new one 

 within or beyond it. Hence the appearance of a full sporangium, sur- 

 rounded by one, or it may be two or three empty ones, one inside the 

 other. (Fig. II, p. 433.) 



This structural feature is peculiar to the genus Saprolegnia among 

 fungi, and it enables mycologists to identify the fungus, of which the 

 pai^yraceous incrustation characteristic of the salmon disease is a 

 product, as a species of that genus. 



Thanks especially to the labors of Pringsheim,* Cornu,t DeBarry,f 



*"Die Entwickelniigs-gescliichte der Achlya prolifera." Nova Acta, 1851, and 

 several later papers iu the Jahrbiicber fur Wissenschaftliche Botanik for 1857, 1860, 

 ami 1874. 



t " MonograpMe " Aimales des Sciences Naturelles, Botanique. 1872. 



t De Barry and Worouiu. " Uutersuchungeu liber die Peronos]Joreen und Sapro- 

 legnien," 1881. 



