114 DORSAL FIN. 



which the animal adheres strongly to any thing in 

 contact with it ; hut to this suhject we shall have 

 to recur presently. The deficiency of ventral fins, 

 as well in so many fishes, as in the cetaceous tribes 

 in general, would go to prove that their use is not, 

 at any rate, a very important one. 



The remaining two fins which we have still to 

 "notice, stand in a difi*erent direction from those we 

 have already illustrated, being perpendicular to the 

 centre of the body, and are employed as balances 

 only, not as organs of progression, or of sinking 

 und rising ; they are, nevertheless, in some species, 

 developed to an extraordinary extent. The dorsal 

 fin is of very varied form, either composed of a few 

 spines only, or it is continued for the whole length of 

 the fish ; it is either single, double, or triple ; and it 

 possesses a degree of consistence so very difi'erent in 

 different species, as to have given occasion, first to 

 Ray and Artedi, and more recently to the late illus- 

 trious Naturalist, the Baron Cuvier, to constitute 

 this a leading distinction between two of the largest 

 families of fishes — the Malacoptert/gii^ or those in 

 which this organ is comparatively soft, and the 

 Acanihopterygn^ or those in which it is hard and 

 spinous. Generally speaking, it is most fully deve- 

 loped in those fishes which inhabit the most stormy 

 seas, while those which are found in comparatively 

 still waters, have this organ much smaller and 

 weaker; but there are many exceptions to this 

 remark. In some fishes, also, it forms a powerful 

 organ of nrotection from the strength of the spines ; 



