THE APODAL ORDER. 213 



more numerous than those of the last, yet they are 

 equally well marked ; nor can they be blended into any 

 other of the classes without a disregard to those natural 

 relations which, as we have already seen, constitute them 

 a primary division. Their slender, cylindrical, and 

 serpent-like body, as seen in the eels (Ang. acutiros- 

 tris Yarr., fig. 38.) generally destitute of scales, and 



covered with slime, separates them, at first sights 

 from the Plectognathes, or cheloniform fishes ; absenc e 

 of ventral fins detaches them equally from the orde r 

 Malacopteryges ; while the softness of their fins, the ray s 

 of which are never spinous, no less separatesthem from the 

 Acanthopteryges. Finally, from both these latter orders 

 they are further distinguished hy having the operculum 

 and branchia concealed j the former being covered with 

 the common skin of the head, which only leaves a small 

 slit or spiracle (a), by which they breathe. This latter 

 is a universal character ; and is the more to be valued, 

 since, whatever eel-shaped or anguilliform fishes are 

 found scattered in other types, even though they may 

 have soft fins, or only the rudiments of ventrals, yet 

 they never have these two characters united with the 

 spiraculated aperture. 



(186.) The Apodes, as we have already shown, 

 occupy that part in the series of fishes which mark 

 the transition from the cartilaginous to the osseous. 

 Hence no definite character for them is to be derived 

 from the nature of their skeleton, except this, indeed, 

 — that a gradual progression in its development may be 

 traced in the different families, from the semi-carti- 



p 3 



