BRANCH CHORD AT A; CLASS F>1$CES : THE PISHES 



brook -lamprey, Lampetra wilder! , is never parasitic. It 

 reaches its full size in larval life and transforms simply 

 for spawning. The sea- and lake-lampreys ascend small 

 fresh-water streams when ready to lay their eggs, few 

 living to return. Sometimes small piles of stones are 

 made for nests. The young undergo a considerable 

 metamorphosis in their development. The largest sea- 

 lampreys reach a length of three feet. The common 

 brook-lampreys are from eight to twelve inches long only. 



The true fishes (Pisces). All the other fish-like ani- 

 mals are grouped in the class Pisces. They are charac- 

 terized, when compared with the lower fish-like forms just 

 referred to, by the presence of jaws, shoulder girdle, and 

 pelvic girdle. The class^includes both the cartilaginous 

 and bony fishes, and is divided into three sub-classes, 

 namely, the Elasmobranchii, including the sharks, rays, 

 skates, torpedoes, etc., the Holocephali, including the 

 chimaeras (a few strange-bodied forms), and the Teleos- 

 tomi, including all the other fishes, as the trout, catfishes, 

 darters, bass, herring, cod, mackerel, sturgeons, etc., etc. 



The sharks, skates, etc. (Elasmobranchii). --The 

 sharks and skates are characterized by the possession of 

 a skeleton composed of cartilage and not bone, as in 

 the bony fishes; they have no operculum; their teeth 

 are distinct, often large and highly specialized, and their 

 eggs are few and very large. There are two principal 

 groups among Elasmobranchii, viz., the sharks, which 

 usually have an elongate body, and always have the gill- 

 openings on the sides, and the rays or skates, which have a 

 broad flattened body with the gill-openings always on the 

 under side. All the members of both groups are marine. 

 The sharks are active, fierce, usually large fishes, which 

 live in the surface-waters of the ocean and make war on 

 other marine animals, all of the species except half a 

 dozen being fish-caters. The shark's mouth is on the. 



