302 



ZOOLOGY 



stroyed before they reach maturity, but there can be httle 

 doubt that vast numbers survive to breed. 



Fishes arc one group of the vertel^rates, or back-boned ani- 

 mals. Vertebrates are characterized })y the possession of an 

 internal skeleton that supports the soft parts of the bodj^, by 

 the possession of two pairs of limbs, and by paired openings 

 leading from the throat to the outside, which last are found 

 in the higher forms in the emliryonic stage only. In the fishes 



p^j' 



Fig. 284. — Salmo fario. a.I, adipose lobe of peh'ic fin; ati, anus; c.f, caudal 

 fin ; d.f.l , first dorsal ; d.f.S, second dorsal or adipose fin ; l.t, lateral line ; op, 

 operculum ; pct.f, pectoral fin ; pv.f, pelvic fin ; v.f, ventral fin. After Jardine. 



these openings are lined by finger-hkc processes into which the 

 blood flows. These are kno^Mr as gills and it is in them that 

 the blood takes ox}'gen from the water. The appendages of 

 fishes are used as paddles in the water and are known as fins. 

 The tail is well developed and, by its powerful side-blows in 

 the water, propels the fish rapidly forward. 



Classification. — Fishes are classified into five groups, the 

 lowest of which contains the lamprejr eels. The next higher 

 in organization (cartilagenous fishes) includes the sharks, 

 skates, and rays.' The third group (the bony fishes) includes 

 the vast majoritj'- of our common fishes. A fourth group — 



1 Fig. 283. 



