HISTORY 
OF 
THE AMERICAN FAUNA. 
FISHES. 
Ichthyology — from fisli, and Pioyoi, dis- 
course — is a term wliicli lias long been in use to 
indicate tliat branch of zoology that treats of the 
lowest class of vertebrate animals. 'I'he word fish 
follows from the Anglo-Saxon Jisc, and is closely 
like the German the Dutch and the Scan- 
dinavian_yfsA 'I’he popular idea of a fish is very in- 
definite. 'J’here are many creatures living in the 
ocean, and in rivers and lakes, that are by no means 
Fishes, but are air-breathing mammals, having warm 
blood, and suckling their young. Some of these 
creatures, though living in the water quite as ha- 
bitually as Fishes — Whales, for example — must yet 
come to the surface to breathe the external air, for 
they have lungs, and not gills. Seals, Porpoises and 
Manatees are of this class, notwithstanding the 
Roman Catholic edict that pronounces their flesh 
“fish,” as a special indulgence. Fishes are cold- 
blooded vertebrates, that inspire air through the 
medium of water in which they dwell ; gills, or bian- 
chiae, accessible through apertures in the sides of the 
head, affording the requisite substitute for the en- 
closed lungs of the land animals. 'I’he delicate, 
branching blood-vessels, that are easily seen on part- 
ing the gill covers, are in immediate contact with 
the water, and receive the vivifying influence of the 
air contained therein, directly, through the constant 
flow taken in at the mouth and forced out at the 
gill openings. 'J’he heart of Fishes is simple, consist- 
ing only of two chambers. 'I’he skeleton of true 
Fishes is provided with a furcula-shaped bone — like the 
“ merry-thought ” of Birds ; and scapular bones, with 
adjunct appendages, are joined together beneath, on 
the medium line. Connected with these bones are 
the pectoral fins, which represent the anterior ex- 
tremities. Other fins are developed singly or un- 
paired, and are made up of rays connected with the 
skeleton, through the intervention of interspinous 
bones that float between the processes of the verte- 
brae. Most Fishes are provided with scales, but in 
some instances the skin is thick and smooth, and 
covered with mucous, which exudes from numerous 
glands that are situated in a row along the sides, 
called the lateral line. Agassiz regarded the other 
species of apertures seen in the sides of Fishes as 
spaces for the admission of water to the circulation. 
through a series of tubes that end in blood-vessels 
near the heart. In the Shad these tubes are easily 
seen. 'I'hey are supposed to be useful in balancing 
the pressure in deep-water Fishes, when suddenly 
changing from shallows to great depths. 'I’he scales 
of Fishes are secreted from little folds of skin. Four 
prominent forms are seen, called, respectively : Cy- 
cloids, those having concentric lines; Glenoids, hav- 
ing toothed edges; Ganoids, having enamelled scales; 
and Placoids, which are large and plate-like; the last 
having the substance called “shagreen,” and in some 
instances the prickles and prominences developed into 
real dentine. 
'I’he hearing iipparatus in Fishes is concealed with- 
in the head. In the Plagiostomes and Gyclostomes 
it is placed in a special cavity, and included in a car- 
tilaginous labyrinth. In the former the canal is pro- 
longed beneath the skin, and extends to the upper 
part of the cranium. In the Rays, also, it is pro- 
longed similarly, and opens externally by several 
small apertures. 'I’he swimming bladder is connected, 
in some instances, with the cranium, through the 
medium of a chain of several small bones. In nearly 
all Fishes there are large semicircular canals, and a 
vestibule connecting with a chamber that contains the 
curiously-formed ossicles or ear-bones, some of which 
are very hard, and others quite limy and soft. The 
eye is seldom provided with eyelids, having free 
edges; some Sharks have a third or nictitating 
membrane. 'I’he organ of smell does not communi- 
cate with the mouth, except in the case of the Myxi- 
noids. 'I’aste is very weak ; though the tongue is 
sufficiently large, it is mostly used for prehension — 
even the teeth are often situated on portions of it. 
'l.’ouch is developed in certain organs, the lips being 
partially possessed of this function. Filaments upon 
the lips and head are probably sensitive, and wai'ii 
the creature of danger, as well as indicate the nature 
of prey. In most osseous Fishes the sexes do not 
come together, but the eggs are sprinkled with milt, 
or seminal fluid. A few bony Fishes are viviparous. 
'I’he Rays and some Sharks are oviparous, their eggs 
being firm and leathery, like those of some reptiles. 
'J’hough Fishes may be said to be especially inhab- 
itants of the waters, yet there are certain variations 
from the rule. It would seem most natural that 
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