106 FISHES 



change of oxygen and carbon dioxide and particularly in 

 those animals which have a thin, moist skin like frogs. 



104. Fishes. — The fishes are vertebrates, that is, they 

 have a notochord which as they develop gives place to a 

 vertebral column. There are four large divisions of fishes 

 (1) the lampreys (lam'priz) and relatives, (2) the sharks 

 and relatives, (3) the bony fishes, and (4) the small 



Figure 108. — Brock Trout. 



group of fishes with lungs. The most important group 

 in numbers and economic importance is the bony fishes. 

 This group- includes the salmon (sam'un), trout, bass, 

 whitefish, pike, shad, menhaden (men-ha/d'n), cod, mack- 

 erel, herring, sardine, etc. Typical bony fishes are the 

 goldfish, perch, and sunfish (Figures 105-108). 



105. External Parts of a Fish. — The external parts of a 

 fish show a well-marked head attached directly to the 

 trunk ; a trunk region, the largest part of the body ; and 

 a tail region which is sometimes as long as the trunk. 



In a bony fish the mouth is at the front end of the 

 head. The jaw bones, bearing many small, needle-like 

 teeth, are not firmly attached to the skull. The side of 



