3 2 4 FISHES. 



scarlet. Writing of those fishes, 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 representatives at the surface. In such fishes the eyes increase 

 in size with the depth inhabited 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 phos- 

 phorescence. In the greatest depths occur blind fishes, with rudimentary eyes, and 

 without special organs of touch. Many fishes of the deep sea are provided with 

 more or less numerous, round, shining, mother-of-pearl-coloured bodies, embedded 

 in the skin. These so-called phosphorescent 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 symmetrically 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 extraordinary 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 them- 

 selves ; 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 

 oldest 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 lung-fishes. 

 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 already described. 



