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THE TEETH OF INVERTEBRATES. 339
leech has two rows of serrations on each jaw ; otlier species doubtless
vary in the buccal armature.
In all the annelids reparation of amputated parts, including the
buccal organs, is common and ap])arently easy. These animals have
existed from very early geological time, and small bodies, supposed to
be the fossilized jaws or " teeth " of annelids, have been found in the
Palaeozoic rocks of both Europe and America.
In insects no true teeth exist. Mandibles and jaws occur in infinite
variety, usually essentially lateral in position and motion, and easily
observed, especially in such forms as the larger grasshoppers and beetles.
Among the spiders teeth are equally absent, the poisonous fangs being
merely modifications of limbs or segmental appendages, as, indeed, are
nearly all the buccal appendages of the annulated or articulated inver-
tebrates.
Among the Crustacea, lobsters, shrimps, crabs, etc., the maxillary
organs are but modifications of entire limbs translated from the locomo-
tive series and set apart as special mouth-organs. Most of the Crustacea
have a suitable masticatory apparatus of this sort, but in certain para-
sitic forms become organs of attachment or are altogether wanting. If
we examine the digestive organs of one of the higher Crustacea, such as
the crab or lobster, we find the stomach divided into two regions, the
anterior or cardiac and the posterior or pyloric region. These are sepa-
FiG. 161.
(From T. Rymer Jones's Outline of the. Animal Kingdom.) Oral Apparatus of Ec.hiniis: a a a a a,
pyramidal pieces forming the lantern of Aristotle ; h ft, internal projections from shell ; c c c c c,
te-th enclosed in their sockets
i i, k k, muscular fasciculi for the movements of the jaw.
rated more by their functions than by their form. The anterior part is
provided with certain masticatory appendages or stomacholiths, often
termed teeth, though more analogous to a sort of calcareous gizzard.
These consist of several calcareous pieces, moved by appropriate mus-
cles, inserted in the membranous wall of the stomach, armed with a
