2692 FISHES 



habits; and are characterized by their generally black or silvery color, although in 

 a few instances the fin rays and certain filaments are scarlet. Writing of those 

 fisher, Dr. Giinther observes that, " the organ of sight is the first to be affected by 

 a sojourn in deep water. Even in fishes which habitually live at a depth of only 

 eighty fathoms, we find the eye of a proportionately larger size than in their repre- 

 sentatives at the surface. In such fishes the eyes increase in size with the depth in- 

 habited by them, down to the depth of two hundred fathoms, the large eyes 

 being necessary to collect as many rays of light as possible. Beyond that depth, 

 small-eyed as well as large-eyed fishes occur; the former having their want of vision 

 compensated by tentacular organs of touch, while the latter have no such accessory 

 organs, and evidently only see by the aid of phosphorescence. In the greatest depths 

 occur blindfishes, with rudimentary eyes, and without special organs of touch. 

 Many fishes of the deep sea are provided with more or less numerous, round, shin- 

 ing, mother-of-pearl-colored bodies, embedded in the skin. These so-called phos- 

 phorescent or luminous organs are either bodies of an oval or irregularly elliptical 

 shape placed in the vicinity of the eyes, or smaller globular bodies arranged sym- 

 metrically in series along the sides of the body and tail." That the function of 

 these bodies is to produce phosphorescent light may be considered certain; and it is 

 probable that both the tentacles and the whole surface of the bodies of these extraor- 

 dinary fish are also phosphorescent. Not the least remarkable feature about the 

 carnivorous deep-sea fishes is the enormous size of their stomachs, which enable 

 them to swallow creatures nearly as large as themselves, drawing themselves over 

 their prey almost after the manner of a sea anemone. Although when brought 

 to the surface deep-sea fishes are soft, flabby creatures, with their scales standing out 

 at right angles, and their eyes starting from their sockets, at their own proper level, 

 under an enormous pressure, their bodies are doubtless as firm and compact as those 

 of ordinary fish. Deep-sea fish certainly live at a depth of two thousand seven 

 hundred and fifty fathoms. 



In regard to geological distribution, it has already been mentioned that the old- 

 est true fishes occur in strata of upper Silurian age; such early fishes being sharks. 

 In the succeeding Devonian and Carboniferous periods, the class was abundantly 

 represented, but only by sharks, fringe-finned ganoids, and lungfishes. In the 

 Permian, Triassic, and Jurassic periods chimseroids, as well as the chondrosteous 

 Teleostomi made their appearance; but it was not till the Cretaceous epoch that the 

 higher bony fishes, which are the predominant forms in the Tertiary period and at 

 the present day, were developed. There are fully nine thousand known species of 

 living fishes, while considerably more than one thousand fossil forms have been al- 

 ready described. 



