6 
FISHES. 
deep ponds, or tarns^ of mountain districts. Of 
Marine Fishes, some roam the wide ocean, some 
play around the coral islands of the tropics, 
others affect the mud, or the sands of the shal- 
lows ; some linger near the estuaries of great 
rivers ; others come in mighty armies around the 
coast at particular seasons, retiring again to the 
deep water in the offing ; finally, some habitually 
keep near the surface, while others rarely rise 
from the vicinity of the bottom. 
The form of a fish is that best calculated to 
facilitate its progression through a fluid medium. 
It is commonly that of a spindle, swelling in the 
middle, and tapering to each extremity. There 
are, it is true, many modifications of this form ; 
some, as the Skates and Flat-fishes, are flattened 
horizontally ; others vertically, as the Chaetodons 
and the Dory ; some are globose, as the Diodons 
and Sun-fishes ; some are drawn out into a ser- 
pent-form, as the Eels and Lampreys ; and some, 
as the Ribbon-fishes, resemble in length and 
thinness the fabrics from which they derive their 
name. Yet, in all these varieties the normal 
form may, without difficulty, be traced. The 
surface of the body is sometimes smooth, or 
covered with a slimy secretion ; occasionally it is 
armed with bony plates, which are sometimes set 
with hard tubercles ; in a few species the body is 
covered with spines, which are capable of being 
laid close to the body, or erected at will ; but the 
general covering of the body forms scales, or 
rounded plates (apparently horny, but considered 
by Professor Owen to be more allied to bone), 
the front margins of which are imbedded in the 
skin, and the posterior margins are loose and 
