with the cold damp earth. It is said that they completely close their
burrows during the winter.
_Structure_. A few remarks must be made on this subject. The body of a
large worm consists of from 100 to 200 almost cylindrical rings or
segments, each furnished with minute bristles. The muscular system is
well developed. Worms can crawl backwards as well as forwards, and by
the aid of their affixed tails can retreat with extraordinary rapidity
into their burrows. The mouth is situated at the anterior end of the
body, and is provided with a little projection (lobe or lip, as it has
been variously called) which is used for prehension. Internally, behind
the mouth, there is a strong pharynx, shown in the accompanying diagram
(Fig. 1) which is pushed forwards when the animal eats, and this part
corresponds, according to Perrier, with the protrudable trunk or
proboscis of other annelids. The pharynx leads into the sophagus, on
each side of which in the lower part there are three pairs of large
glands, which secrete a surprising amount of carbonate of lime. These
calciferous glands are highly remarkable, for nothing like them is known
in any other animal. Their use will be discussed when we treat of the
digestive process. In most of the species, the sophagus is enlarged
into a crop in front of the gizzard. This latter organ is lined with a
smooth thick chitinous membrane, and is surrounded by weak longitudinal,
but powerful transverse muscles. Perrier saw these muscles in energetic
action; and, as he remarks, the trituration of the food must be chiefly
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 {17} 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.
[Picture: Fig. 1: Diagram of the alimentary canal of an earth-worm. Fig.
2: Tower-like casting from near Nice]
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