58 ANIMAL FORMS 
driving a current from the body-cavity fluids, which wash 
the wastes to the exterior. 
59. Nervous system.—The nervous system of the earth- 
worm consists first of a brain composed of two pear-shaped 
masses united together above the pharynx (one shown in 
Fig. 34), from which nerves pass out to the upper lip and 
the head, which are thus rendered highly sensitive. Two 
other nerves also pass out from the brain, and, coursing 
down on each side of the pharynx like a collar, unite below 
it and extend side by side along the under surface of the 
digestive system throughout its entire extent. In each 
segment the two halves of this ventral nerve-cord are united 
by a nerve, and others are distributed to various organs, 
which are thus made to act and in proper amount for the 
good of the body as a whole. 
In its relation to the outside world the chief source of 
information comes to the earthworm through the sense of 
touch, for definite organs of sight, taste, and smell are but 
feebly developed, while ears appear to be entirely absent. 
Nevertheless these are sufficient to enable it to lead a suc- 
cessful life, as is evidenced by the great number of such 
forms found on every hand. 
60. Egg-laying.—In digging up the soil where earth- 
worms abound one frequently finds small yellowish or 
brownish bodies looking something like a grain of wheat. 
These are the cocoons in which the earthworms lay their 
eggs, and the method by which this is performed is unique. 
We have already noted the presence of a swollen girdle 
(the clitellwm) about the body of the worm. At the breed- 
ing season this throws out a fluid which soon hardens into 
an encircling band. By vigorous contractions of the body 
this horn-like collar is now slipped forward, and as it passes 
the openings of the reproductive organs the eggs and 
sperms are pushed within it. They thus occupy the space 
between the worm and the collar, and when the latter is 
shoved off over the head its ends close as though drawn to- 
