FISHES. 605 
Their chief organ of natation is the caudal fin, but they are 
distinguished from all other fishes by the manner in which they use 
this oar. When turned upon their side this organ is not horizontal, but 
vertical, and strikes the water vertically upand down. They advance 
through the water but very slowly, compared to the motion of other 
fishes. They ascend or descend in the water with great promptitude, 
but they cannot turn to the right or left with the same facility as other 
fishes. ‘This property of rising or sinking in the water with facility is 
the more useful to them, inasmuch as the greater part of their existence 
is passed at the greatest depths, where they draw themselves along the 
Fig. 385.—The Sand-eel (Ammodytes ancea) 
° 
sands at the bottom of the sea, and often hide themselves from their 
enemies. Among the P/euronectida, soles, turbot, flounders, and 
plaice may be noted. 
The soles have the body oblong, the snout is round, nearly always 
in advance of the mouth, which is twisted to the left side and furnished 
with teeth on one side only, while the eyes are on the right side. The 
dorsal fin commences about the mouth, and extends up to the caudal 
or terminal fin. The Common Sole, Sola vulgaris (Fig. 386), is 
plentiful in the Channel, along our coasts, and especially in the 
Mediterranean. It is brown on the right and whitish on the opposite 
side. Its pectoral fins are spotted black; the scales rugged and 
denticulate ; its size seems to vary according to the coast it frequents. 
Off the mouth of the Seine soles are sometimes taken eighteen and 
twenty inches in length, There are several modes of taking them, 
