PISCES 



475 



hosts in order to ensure the continuance of the species. No 

 less than six species of Echinorhynchi are known to infest the 

 trout (Salmo fario). As many as four species likewise infest 

 the eel (Anguilla) ; the same number of distinct forms being 

 also found in the turbot (Rhombus) and ling (Lota), whilst 

 three species may be met with in the common sole (Solea). 

 What we at present know respecting the mode of development 

 of Echinorhynchi infesting fishes is principally due to the 

 researches of Leuckart. Some years back Dr Guido Wagener 



FIG. 84. 1, Echinorhynchus angustatus (natural size and enlarged) ; 2, Echinorhynchut 

 nodulosus (natural size and enlarged), with (3) two eggs (magnified 1000 diameters). 

 Both species from a trout. After Busk. 



supplied admirable illustrations of the eggs and embryos of 

 Echinorhynchi, but he was erroneously led to conclude that the 

 larvas were developed in a direct manner. The notion of a 

 simple metamorphosis was entirely disproved by the experi- 

 ments of Leuckart, who found the growth and development of 

 the young to be accompanied by a true alternate generation. 

 He showed this to obtain in Echinorhynchus proteus, a species 

 abundant in the trout and in many other fresh- water fishes. The 



