28 1 2 THE BONY FISHES AND GANOIDS 



There is a separate short first dorsal fin, followed, after a short interval, by a very 

 long and low second dorsal, which is composed of very weak rays, and is continued 

 to the end of the tail; the anal occupying a precisely similar position on the under 

 surface, and the thoracic or jugular pelvic fins consisting of several rays. Dr. 

 Giinther writes that ' ' this family, known a few years ago from a limited number of 

 examples, representing a few species only, proves to be one which is distributed 

 over all oceans, occurring in considerable variety and great abundance at depths of 

 from one hundred and twenty to two thousand six hundred fathoms. They are, in 

 fact, deep-sea gadoids, much resembling each other in the general shape of the 

 body, but differing in the form of the snout, and in the structure of their scales. 

 About forty species are known, many of which attain a length of three feet." 



THE FLATFISHES Family PLEURONECTID^ 



Distinguished by the unsymmetrical conformation of the head and anterior 

 region of the body in the adult, in consequence of which both eyes are brought on 

 to one side of the body (in some cases the right, and in others the left), the flat- 

 fishes differ not only from all other members of their class, but likewise from all 

 other vertebrates. The body is strongly compressed and flattened, with the side 

 which is turned upward, and on which are situated the eyes, colored dark, while 

 the opposite, or eyeless side is, as a rule, colorless. The bones of the head are 

 unequally developed and unsymmetrical; and the dorsal and anal fins are of 

 great length, and undivided, the former often extending forward so as to separate 

 the blind from the eyed side of the head. In the most specialized forms the teeth 

 and jaws are more developed on the lower or blind side than on the other, and there 

 is no air bladder. Dr. Cunningham, who has paid special attention to the structure 

 of these fishes, writes that "mere dissection of adult specimens show that the 

 anomalous position of the eyes is due to a distortion of the facial region of the skull. 

 The cranial region of the skull is but slightly altered, but the interorbital parts of 

 the two frontal bones are bent away from their original position in the dorsal 

 median line down to the side of the head, and they are also compressed into a thin 

 plate. But the eyes have pretty nearly the same relation to the interorbital septum 

 as in an ordinary fish. There is one eye on each side of the septum as usual. It 

 is, in fact, the curious condition of the dorsal fin in the flatfish, even more than the 

 mere distortion of the eyes, which makes it so different from the ordinary fish. If 

 the fin terminated some distance behind the eyes, or if it was prolonged in the 

 direction it ought to follow, that is along the line which divides the two frontal 

 bones from one another, it would be plain at a glance which was the left side of the 

 head and which the right. It would then be obvious that the left eye was still on 

 the left side of the head, and the right eye on the right. But the dorsal fin does 

 neither of these things. The external ethmoid bone belonging to the blind side is 

 much enlarged, and sends back a process outside the eye belonging to that side to 

 meet another process from the cranial region of the skull. Thus the eye which has 

 migrated the upper eye when the fish is held in a vertical plane is inclosed in a 



