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History of Animals   

Of swimming creatures that are destitute of feet, some have
winglets or fins, as fishes: and of these some have four fins, two
above on the back, two below on the belly, as the gilthead and the
basse; some have two only,-to wit, such as are exceedingly long and
smooth, as the eel and the conger; some have none at all, as the
muraena, but use the sea just as snakes use dry ground-and by the way,
snakes swim in water in just the same way. Of the shark-kind some have
no fins, such as those that are flat and long-tailed, as the ray and
the sting-ray, but these fishes swim actually by the undulatory motion
of their flat bodies; the fishing frog, however, has fins, and so
likewise have all such fishes as have not their flat surfaces
thinned off to a sharp edge.
Of those swimming creatures that appear to have feet, as is the
case with the molluscs, these creatures swim by the aid of their
feet and their fins as well, and they swim most rapidly backwards in
the direction of the trunk, as is the case with the cuttle-fish or
sepia and the calamary; and, by the way, neither of these latter can
walk as the poulpe or octopus can.
The hard-skinned or crustaceous animals, like the crawfish,
swim by the instrumentality of their tail-parts; and they swim most
rapidly tail foremost, by the aid of the fins developed upon that
member. The newt swims by means of its feet and tail; and its tail
resembles that of the sheatfish, to compare little with great.
Of animals that can fly some are furnished with feathered wings,
as the eagle and the hawk; some are furnished with membranous wings,
as the bee and the cockchafer; others are furnished with leathern
wings, as the flying fox and the bat. All flying creatures possessed
of blood have feathered wings or leathern wings; the bloodless
creatures have membranous wings, as insects. The creatures that have
feathered wings or leathern wings have either two feet or no feet at
all: for there are said to be certain flying serpents in Ethiopia that
are destitute of feet.
Creatures that have feathered wings are classed as a genus
under the name of 'bird'; the other two genera, the leathern-winged
and membrane-winged, are as yet without a generic title.
Of creatures that can fly and are bloodless some are coleopterous
or sheath-winged, for they have their wings in a sheath or shard, like
the cockchafer and the dung-beetle; others are sheathless, and of
these latter some are dipterous and some tetrapterous: tetrapterous,
such as are comparatively large or have their stings in the tail,
dipterous, such as are comparatively small or have their stings in
front. The coleoptera are, without exception, devoid of stings; the
diptera have the sting in front, as the fly, the horsefly, the gadfly,
and the gnat.
Bloodless animals as a general rule are inferior in point of size
to blooded animals; though, by the way, there are found in the sea
some few bloodless creatures of abnormal size, as in the case of
certain molluscs. And of these bloodless genera, those are the largest
that dwell in milder climates, and those that inhabit the sea are
larger than those living on dry land or in fresh water.
All creatures that are capable of motion move with four or more
points of motion; the blooded animals with four only: as, for
instance, man with two hands and two feet, birds with two wings and
two feet, quadrupeds and fishes severally with four feet and four
fins. Creatures that have two winglets or fins, or that have none at
all like serpents, move all the same with not less than four points of
motion; for there are four bends in their bodies as they move, or
two bends together with their fins. Bloodless and many footed animals,
whether furnished with wings or feet, move with more than four
points of motion; as, for instance, the dayfly moves with four feet
and four wings: and, I may observe in passing, this creature is
exceptional not only in regard to the duration of its existence,
whence it receives its name, but also because though a quadruped it
has wings also.

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