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.

    All animals move alike, four-footed and many-footed; in other
words, they all move cross-corner-wise. And animals in general have
two feet in advance; the crab alone has four.

                                   6

    Very extensive genera of animals, into which other subdivisions
fall, are the following: one, of birds; one, of fishes; and another,
of cetaceans. Now all these creatures are blooded.

    There is another genus of the hard-shell kind, which is called
oyster; another of the soft-shell kind, not as yet designated by a
single term, such as the spiny crawfish and the various kinds of crabs
and lobsters; and another of molluscs, as the two kinds of calamary
and the cuttle-fish; that of insects is different. All these latter
creatures are bloodless, and such of them as have feet have a goodly
number of them; and of the insects some have wings as well as feet.

    Of the other animals the genera are not extensive. For in them
one species does not comprehend many species; but in one case, as man,
the species is simple, admitting of no differentiation, while other
cases admit of differentiation, but the forms lack particular
designations.

    So, for instance, creatures that are qudapedal and unprovided
with wings are blooded without exception, but some of them are
viviparous, and some oviparous. Such as are viviparous are
hair-coated, and such as are oviparous are covered with a kind of
tessellated hard substance; and the tessellated bits of this substance
are, as it were, similar in regard to position to a scale.

    An animal that is blooded and capable of movement on dry land,
but is naturally unprovided with feet, belongs to the serpent genus;
and animals of this genus are coated with the tessellated horny
substance. Serpents in general are oviparous; the adder, an
exceptional case, is viviparous: for not all viviparous animals are
hair-coated, and some fishes also are viviparous.

    All animals, however, that are hair-coated are viviparous. For,
by the way, one must regard as a kind of hair such prickly hairs as
hedgehogs and porcupines carry; for these spines perform the office of
hair, and not of feet as is the case with similar parts of
sea-urchins.

    In the genus that combines all viviparous quadrupeds are many
species, but under no common appellation. They are only named as it
were one by one, as we say man, lion, stag, horse, dog, and so on;
though, by the way, there is a sort of genus that embraces all