278 



THE FRESH-WATEE FISHES OF EUROPE. 



which is closely allied to the Peronospora, which causes potato disease the 

 one type always being limited to plants, and the other to animals. 



Professor Huxley proved the nature of the disease by cultivating the fungus 

 on the bodies of dead flies, and therefore demonstrated that neither pollution, 

 nor drought, nor over-stocking, will produce Salmon disease if the Saprolegnia 

 is absent. By a simple arithmetical calculation of the number of spores, it is 

 shown that a single diseased fly might render a shallow stream dangerous to 

 Salmon for several days, while forty large fully diseased Salmon would 

 furnish one spore to every gallon of the 380,000,000 gallons which every 

 day flow over Teddington Weir in the Thames. There is no known remedy for 

 the disorder. 



Multitudes of Kelts die annually from the exhaustion consequent on 

 spawning. 



TROUT. 



We have arranged the Trout according to the number of fin rays, and give 

 in the following table a summary of characters which exhibit the resemblances 

 of the chief types with each other. 



TABLE OF THE PRINCIPAL EUROPEAN SPECIES OF TROUT. 

 Arranged according to the number of rays in the jim. 



