THE WORMS, 55 
ANNELIDS OR SEGMENTED Worms 
55. The earthworms and their relatives—Leaving the 
groups of the parasitic animals, which have been driven from 
the field of active existence and in many ways are degraded 
by such a mode of life, we pass on to the higher free-living 
worms, where brilliant colors, peculiar habits, or remarkable 
adaptations render them peculiarly interesting. In consid- 
ering first their general organization, we may use the earth- 
Fig. 38.—Earthworm (Lumbricus terrestris). m, mouth ; ¢, girdle or clitellum. 
worm (Fig. 33) (sometimes called angle-worm or fish-worm) 
as a type because of its almost universal distribution. 
The body is cylindrical, shows well-marked dorsal and 
ventral surfaces, and, as in all of the annelids, is jointed, 
each joint being known as a segment. Anteriorly it tapers 
to a point, and the head region bearing the mouth is ill- 
defined, unlike many sea forms, yet serves admirably for 
tunneling the soil in which all earthworms live. In this 
process the animal is also aided by bristles or sete which 
project from the body wall of almost every segment and 
may be stuck into the earth to afford a foothold. 
56. Food and digestive system.—The earthworms are 
nocturnal animals, seldom coming to the surface during the 
day except when forced to do so by the filling of their tun- 
nels with water or when pursued by enemies. At night 
they usually emerge partially, keeping the posterior end of 
the body within the burrow, and thus they scour the sur- 
rounding areas for food, which they appear, in some cases 
at least, to locate by a feeble sense of smell. They also 
frequently extend their habitations, and in so doing swallow 
enormous quantities of earth from which they digest out 
any nutritive substances, leaving the indigestible matter in 
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