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, 

 whichare 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 clitellum] 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- 



