CHAPTER I 



FISHES: THEIR GENERAL CHARACTER 

 AND STRUCTURE 



Respiration— General Structure — The Air-Bladder — Fins — An Exception in 

 the Flat- Fishes— Pectoral and Ventral Fins — The Vertical Fins — 

 Divisions of the Body — External Design— Locomotion and its Organs 

 — Scales — The Lateral Line. 



To all mammals, birds, and to many reptiles, insects, and other 

 animals, oxygen dissolved in water is useless for purposes of 

 respiration ; and although there are certain warm-blooded 

 vertebrate creatures, so remotely related to each other in the 

 modern system of classification as the whale, the manatee, and 

 the seal, which, having made the water their permanent habita- 

 tion, have acquired many of the external characteristics of fish, 

 yet all of these depend for existence upon periodical draughts 

 of fresh air. Some reptiles and insects pass through their 

 earlier metamorphoses, from egg to larva and pupa, in the 

 water ; but on reaching the ultimate or perfect stage, they lose 

 the peculiar apparatus which enables them to extract oxygen 

 from their native medium ; they spend the rest of their lives 

 breathing free air as terrestrial animals, and although they 

 must visit the water to deposit therein the ova upon which 

 the perpetuation of their species depends, they cannot remain 

 submerged except on pain of death. 



The class of Fishes, on the other hand, consists of those 

 vertebrate animals which inhabit salt or fresh water, extracting 

 therefrom the oxygen necessary to their existence by means of 



