68 BRANCH ANNULATA 



ing it forward, since the setae prevent its moving backward. 

 When the earthworm moves backward the setae are directed 

 forward, and the same processes propel the worm backward. 



Excretion. — In all the segments of the body except the first 

 three and the posterior one is a pair of tubular kidneys (nephri- 

 dia). Each begins in a ciliated funnel — which opens into and 

 takes up the waste from the body cavity — in the back part of a 

 segment, and continues in a long, much-looped tube, which 

 opens externally by a small excretory pore on the ventral 

 surface of the segment posterior to the one in which the funnel- 

 shaped beginning is situated. 



Multiplication. — The earthworm is hermaphroditic, but 

 cross-fertilization takes place. The lateral and dorsal portions 

 of the segments from the thirty-second to the thirty-seventh 

 are swollen and somewhat fused together, forming a sort of 

 girdle (the clitellum). The glands of this clitellum secrete a 

 viscid fluid. This secretion hardens, upon exposure to the air, 

 and forms a band or collar about the clitellum. This collar 

 moves forward, gathers the eggs and sperms^ as it passes the 

 openings, and finally is slipped off over the head.^ The ends of 

 the collar now close and it forms a tough egg-capsule. The 

 egg-capsules are hidden under stones, boards, or logs, or are 

 buried in the earth, especially about barnyards and compost 

 heaps. " The worms are about 1 inch long when hatched."' 



They hibernate below the frost line in winter. 



Enemies. — The chief enemies are moles and birds. To 

 avoid the birds they feed at night or early morning, and some- 

 times drag a pebble into the mouth of the burrow, closing it 

 after them. 



The marine worms (Polyche'ta) are dioecious, and the young undergo a 

 more or less complete metamorphosis. The larva is a trochoxpherc* Some 

 burrow in the sand; some are free swimming; some secrete a mucus which 

 hardens and forms tubes; others form tubes by sticking together with 

 mucus pieces of shell, sand, mud, or limestone. ^lost of the tube-building 

 species are fixed to some object, but a few carry their tubes about. JMany 

 of these marine worms live in shallow water, but some have been found 

 at a depth of 3000 fathoms. 



' These have been obtained from another earthworm. 

 2 Shipley and MacBride, p. 100. 

 ' Colton, " Descriptive Zoology." 

 * See Glossary 



