I. INTESTINAL Are simple and naked, without limbs; some of them live
within other animals, as the _ascarides_ and _tape-worms_; others in
water, as the _leeches_; and a few in the earth, as the _earth-worm_.
II. MOLLUSCOUS Are simple animals, without shell, and furnished with
limbs, as the _cuttle-fish_, _medusæ_, _star-fish_, and _sea-urchins_.
III. TESTACEOUS Are animals similar to the last, but covered with shells,
as _oysters_, _cockles_, _snails_, and _limpets_.
IV. ZOOPHYTES Are composite animals, and appear to hold a rank between
animals and vegetables; though they are in fact true animals, and possess
sensation and voluntary motion. In many instances a great number of them
inhabit the same stone, but some are soft, naked, and separate. The
_coral_, _sponge_, and _polypes_, are instances of this order.
V. ANIMALCULES Are destitute of tentacula or feelers, and are generally
so minute as to be invisible to the naked eye. They are chiefly found in
different infusions of animal and vegetable substances.
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