effected by this organ, for worms possess no jaws or teeth of any
kind. Grains of sand and small stones, from the 1/20 to a little
more than the 1/10 inch in diameter, may generally be found in
their gizzards and intestines. As it is certain that worms swallow
many little stones, independently of those swallowed while
excavating their burrows, it is probable that they serve, like
mill-stones, to triturate their food. The gizzard opens into the
intestine, which runs in a straight course to the vent at the
posterior end of the body. The intestine presents a remarkable
structure, the typhlosolis, or, as the old anatomists called it, an
intestine within an intestine; and Claparede {13} has shown that
this consists of a deep longitudinal involution of the walls of the
intestine, by which means an extensive absorbent surface is gained.

The circulatory system is well developed. Worms breathe by their
skin, as they do not possess any special respiratory organs. The
two sexes are united in the same individual, but two individuals
pair together. The nervous system is fairly well developed; and
the two almost confluent cerebral ganglia are situated very near to
the anterior end of the body.

Senses.--Worms are destitute of eyes, and at first I thought that
they were quite insensible to light; for those kept in confinement
were repeatedly observed by the aid of a candle, and others out of
doors by the aid of a lantern, yet they were rarely alarmed,
although extremely timid animals. Other persons have found no
difficulty in observing worms at night by the same means. {14}

Hoffmeister, however, states {15} that worms, with the exception of
a few individuals, are extremely sensitive to light; but he admits