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History of Animals   


Some species of birds are furnished additionally with spurs,
but no bird with crooked talons is found so provided. The birds with
talons are among those that fly well, but those that have spurs are
among the heavy-bodied.
Again, some birds have a crest. As a general rule the crest sticks
up, and is composed of feathers only; but the crest of the barn-door
cock is exceptional in kind, for, whereas it is not just exactly
flesh, at the same time it is not easy to say what else it is.
13

Of water animals the genus of fishes constitutes a single group
apart from the rest, and including many diverse forms.
In the first place, the fish has a head, a back, a belly, in the
neighbourhood of which last are placed the stomach and viscera; and
behind it has a tail of continuous, undivided shape, but not, by the
way, in all cases alike. No fish has a neck, or any limb, or testicles
at all, within or without, or breasts. But, by the way this absence of
breasts may predicated of all non-viviparous animals; and in point
of fact viviparous animals are not in all cases provided with the
organ, excepting such as are directly viviparous without being first
oviparous. Thus the dolphin is directly viviparous, and accordingly we
find it furnished with two breasts, not situated high up, but in the
neighbourhood of the genitals. And this creature is not provided, like
quadrupeds, with visible teats, but has two vents, one on each
flank, from which the milk flows; and its young have to follow after
it to get suckled, and this phenomenon has been actually witnessed.
Fishes, then, as has been observed, have no breasts and no
passage for the genitals visible externally. But they have an
exceptional organ in the gills, whereby, after taking the water in the
mouth, they discharge it again; and in the fins, of which the
greater part have four, and the lanky ones two, as, for instance,
the eel, and these two situated near to the gills. In like manner
the grey mullet-as, for instance, the mullet found in the lake at
Siphae-have only two fins; and the same is the case with the fish
called Ribbon-fish. Some of the lanky fishes have no fins at all, such
as the muraena, nor gills articulated like those of other fish.
And of those fish that are provided with gills, some have
coverings for this organ, whereas all the selachians have the organ
unprotected by a cover. And those fishes that have coverings or
opercula for the gills have in all cases their gills placed
sideways; whereas, among selachians, the broad ones have the gills
down below on the belly, as the torpedo and the ray, while the lanky
ones have the organ placed sideways, as is the case in all the
dog-fish.
The fishing-frog has gills placed sideways, and covered not
with a spiny operculum, as in all but the selachian fishes, but with
one of skin.
Morever, with fishes furnished with gills, the gills in some
cases are simple in others duplicate; and the last gill in the
direction of the body is always simple. And, again, some fishes have
few gills, and others have a great number; but all alike have the same
number on both sides. Those that have the least number have one gill
on either side, and this one duplicate, like the boar-fish; others
have two on either side, one simple and the other duplicate, like
the conger and the scarus; others have four on either side, simple, as
the elops, the synagris, the muraena, and the eel; others have four,
all, with the exception of the hindmost one, in double rows, as the
wrasse, the perch, the sheat-fish, and the carp. The dog-fish have all
their gills double, five on a side; and the sword-fish has eight
double gills. So much for the number of gills as found in fishes.
Again, fishes differ from other animals in more ways than as
regards the gills. For they are not covered with hairs as are
viviparous land animals, nor, as is the case with certain oviparous
quadrupeds, with tessellated scutes, nor, like birds, with feathers;

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