176 SEGMENTED WORMS— THE ANNELIDS 



pores of the seminal receptacles, sperms which have been received from 

 the other worm are discharged and fertilize the eggs. The cocoon 

 passes over the head and the ends close up tightly. It is left just be- 

 neath the surface of the ground by the worm. After completing their 

 embryological development, the young worms crawl out of the cocoon 

 (only one develops in each capsule in Lumbricus terrestris) . 



There is no asexual means of reproduction, but the power of regen- 

 eration is still possessed to a great degree even though diminished be- 

 cause of the greater specialization of cells in the earthworm's body. 

 If an earthworm is cut in two between segments 15 and 18, the head 

 piece will regenerate a new tail and the tail piece, a new head. If the 

 cut is made posterior to segment 18, the tail piece cannot regenerate a 

 new head, but instead usually develops another tail to form a worm with 

 a tail on either end. This earthworm can very easily take care of eges- 

 tion, but is at a loss for a place of ingestion and must slowly starve to 

 death. 



As in planaria, grafting is possible and an exceptionally long worm 

 can be produced by grafting the posterior end of one worm onto the end 

 of another earthworm, or a short one can be made by cutting several 

 inches out of the center of one and grafting the two ends together. 

 Curious two-headed or two-tailed monsters can be made by grafting 

 together appropriate parts of several earthworms. 



A Marine Annelid — The Clam Worm 



The clam worm, Neanthes, is representative of the many marine an- 

 nelids. This worm lives in the sand of shallow water near the shore 

 line of many of the sandy beaches of the world. It burrows down into 

 the sand, leaving only its head and tentacles protruding. Whenever 

 some small water animal ventures too close to this innocent-looking 

 protrusion, the clam worm may throw out its proboscis, grasp the ani- 

 mal, and pull it down into the burrow where it will be devoured. In 

 external appearance the clam worm differs rather strikingly from the 

 earthworm because of the presence of a row of paddle-like parapodia 

 on each side of the body. There is a pair of these appendages on each 

 segment. They are used in swimming and also to keep a current of 

 water flowing through the burrow when the animal is at rest. This is 

 necessary for proper respiration. 



The body systems of the clam worm are very much like those of the 

 earthworm except for reproduction. The clam worm has separate sexes, 

 and the reproductive cells develop from the wall of the coelom in the 

 posterior region of the body. During the reproductive season this por- 



