AN EARTHWORM 67 
ANNELIDA 
AN OLIGOCHAETOUS ANNELID. AN EARTHWORM 
The earthworm is, to most people, the most familiar annelid. 
It is distributed over the entire earth, the United States contain- 
ing many species. The animal is nocturnal in its habits. It lives 
in long burrows in the ground, in which it lies during the day and 
the inclement seasons of the year. Its food consists of leaves 
and other vegetable substances and also of the organic matter 
contained in the soil which passes through its alimentary canal. 
Study the animal first alive, but have one also at hand which 
has been killed in weak alcohol. Notice its color, or rather 
lack of color. How is this correlated with its underground 
life? Note its cylindrical, elongated body, the very small head, 
and the absence of appendages. Note also the absence of a 
hard shell, the external integumentary covering being the glis- 
tening cuticula which has not been stiffened by the presence of 
calcareous salts. As the animal lacks appendages, locomotion is 
accomplished by means of body-movements. Study its method 
of locomotion. The animal will be observed successively to 
elongate and to shorten its body, which, of course, would be 
impossible if it were covered by a hard shell. Notice that along 
the ventral and the lateral surfaces are several rows of minute 
bristles, the sete; they aid in locomotion and are under the 
control of muscles. Determine, by passing the animal through 
the fingers and with the aid of a hand lens, how many rows there 
are and their relation to the segments. Determine also whether 
the set at the forward end of the body project in the same 
direction as those at the hinder end. Observe carefully the 
importance of the setz in locomotion. 
