extensive coating of fine, short, white hyphse, set so close 

 together that they look like a close-cropped turf. These 

 filamentous hyphae grow with great rapidity, and spread 

 more and more widely. Their increasing weight gradually 

 drags the fly's body down, until it becomes completely sub- 

 merged, and at length sinks to the bottom, invested by a 

 white ball formed by the hyphae, which radiate on all sides 

 from its body. 



Microscopic examination now shows that these hyphae 

 perforate the tough cuticle of the fly, and ramify in the 

 interior of its body, destroying and appropriating the tissues. 

 O n their outer free ends, on the other hand, a large number 

 of the hyphae are terminated by a sort of fruit (sporangium) 

 in which the minute bodies (zoospores) which play the part 

 of seeds or germs are formed, and from which they are 

 eventually discharged. The comparison of the characters 

 of the sporangia and spores with those of Saprolegnia ferax 

 will leave no doubt that the fungus thus transmitted from 

 the fish to the fly is of that species. 



In order to complete the chain of proof, it was necessary 

 to give the disease to fish by infecting them with Saprolegnia 

 from the insect. As I had very little time to devote to the 

 experiments requisite for this purpose, I requested my friend 

 Mr. George Murray, of the Botanical Department of the 

 British Museum, to join with me in making them. Our first 

 attempts yielded negative results, but, on the 2nd of March, 

 1883, Mr. Murray rubbed a saprolegnized fly on the left 

 flanks of two healthy dace, at a spot about the middle of 

 the length of the body. 



"On the 5th of March," Mr. Murray reports, "each of 

 these fish had a small tuft of what was afterwards found to 

 be Saprolegnia ferax growing on the region of inoculation, 

 and, by the loth of March, it had grown into a large patch." 



