3 2 4 
FISHES. 
scarlet. Writing of those fishes, Dr. Gunther 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 smarting 
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. 
