MARINE VERTEBRATES 323 



These fishes are particularly interesting on account of their 

 gregarious habits and the enormous size of the shoals they form, a 

 single shoal often containing millions of individuals ; and they are 

 often captured in such quantities that large numbers are sold to 

 farmers as manure to enrich the soil. The shoals are followed 

 closely by many larger carnivorous species that devour them in great 

 numbers, as well as by flocks of sea birds that prey on them, and 

 yet their numbers are not appreciably reduced by such ravages. 

 They spawn in shallow waters near the coast, and feed principally 

 on the crustaceans and worms of the littoral zone. 



Sprats were once considered to be the young of the Herring, 

 but it is now universally acknowledged that they are a distinct 

 species, and quite a number of characteristics have been given as 

 a means of distinguishing between the two. The young of the 



FIG. 232. THE COMMON EEL 



herring are, however, used largely as food, for that miscellaneous 

 mixture of fry and small species known as Whitebait consists largely 

 of these and the young of the sprat. 



Herrings are captured principally off the north and east 

 coasts, but the pilchards, which are often confused with them, 

 and even at times sold under the same name, are caught chiefly off 

 the coast of Cornwall. 



Although the Eels (Anguillidce) are so readily distinguished by 

 their general form and appearance, yet it may be advisable to call 

 attention to one or two of the leading characters that would possibly 

 be overlooked by an ordinary observer, and in doing this we ask 

 the reader to note that our remarks apply to the true eels only, 

 and not to the sand eels and other fish that may be confused with 

 them. 



The elongated bodies of the Anguillidce are covered with a 



