318 VERTEBRATES: FISHES. 



SECTION V. 



THE CLASS OF FISHES. 



THE Class of Fishes comprises cool-blooded vertebrates 

 which live exclusively in water, and whose respiration is 

 effected in that medium by means of gills. Though living 

 in a liquid of nearly the same specific gravity as them- 

 selves, they are adapted, by their whole structure, for 

 easy motion, and for the most rapid progression. The 

 limbs corresponding to the locomotive members of higher 

 vertebrates are comparatively little developed, and are 

 called fins. The parts corresponding to arms and legs 

 are extremely short, or entirely concealed. The parts 

 corresponding to fingers and toes are called rays, and 

 serve as supports to the membranous parts of the fins. 

 Those fins which correspond to the anterior locomotive 

 members of higher vertebrates are called pectorals, and 

 those which correspond to the posterior, ventrals. Be- 

 sides the pectorals and ventrals, there are other fins which 

 are vertical. Those upon the back are called dorsal, 



Fig. 173. 



p 



/, pectorals ; v, ventrals ; d, dorsal ; a, anal ; c, caudal 



those beneath the tail anal, and the fin at the end of the 

 tail caudal. Most of this class are scaly, but some are 

 naked, others spinous, and others still are mailed. The 

 head of Fishes varies much in form, and consists of a 

 greater number of bones than are found in other ovipa- 



