THE BANDED OPHISURUS. 8? 



are entirely conducted by the spine. The form of 

 these fish is very similar to that of a snake, as their 

 names imply ; and even the pectoral fins are ex- 

 tremely small in proportion, compared with those 

 of fishes having the same lengthened form. These 

 and the true eels can move very rapidly through the 

 water, but when undisturbed upon the bottom, 

 their motions have more the aspect of crawling 

 than of swimming. 



We shall now notice, with more detail, the cases 

 of the various fins, as they are connected with the 

 spinal column, and as instrumental to the loco- 

 motion of fishes. And we shall first describe the 

 tail) or caudal fin, as by far the most important 

 organ in active progression; for, in rapid move- 

 ments through the water, it must be at once per- 

 ceived that the fish could not possibly move any of 

 its fins so as to act as propelling powers, for if, 

 at any period, they projected at angles from the 

 sides of the animal, they would materially ob- 

 struct its motion. The tail, in the greater number 

 of osseous fishes, consists of a series of jointed rays 

 fixed to flat bones, which are, again, articulated to 

 the last joint of the vertebral column. These rays 

 are connected by a web, and ordinarily exhibit a 

 flat fan or paddle; and it is the elongation or 

 shortening of these rays, with the form of the in- 

 tervening web, which occasions the almost endless 

 variation which we see in the shape of this organ. 

 The structure which is most conducive to a swift 

 motion, as well as to the power of keeping up a 



