b THE AJSTGLER-NATUKALIST. 



CHAPTER II. 



GENERAL OUTLINES OF ICHTHYOLOGY. 



OBGANIZATION OF FISH. — BBBATHING-APPAKATUS. — TEMPEBATUEE 

 OF BLOOD. — SIGHT. — HEARING. — PEELING. — SHELL. — TASTE. — 

 AFFECTIONS. — OEGANS OP DIGESTION. — THE BHAIN. — THE SWIM- 

 BLADDEE. — SEXUAL DISTINCTIONS. — OEGANS OP EEPBODUCTION. 

 — SCALES : FOEMATION AND USES. — MODE OP PEOPULSION. — 

 BONES. — PINS. — TBBTH. 



Fishes form the fourth or lowest class of vertebrate 

 animals (i. e. animals possessing a back-bone) in the great 

 systematic division of the Animal Kingdom ; and from the 

 fact that the salt waters alone occupy more than seven- 

 tenths of the globe's entire surface, and are in all proba- 

 bility inhabited, stratum super stratum, as far as, or even 

 further down than the rays of the sun can penetrate, it will 

 readily be conceived that they are not only the most nume- 

 rous of all vertebrate animals, but must infinitely exceed in 

 numbers the whole of the other three classes of the same 

 grand division. 



What may be the precise depth of these ocean fields 

 at which life ceases and the profound of darkness and 

 death begins, we have no direct means of ascertaining. It 

 necessarily varies, however, with the latitude, being greater 

 as the rays of the sun are more direct, and less as their 

 obliquity increases, and it probably also varies with the 

 nature of the bottom. 



