WORMS 



47 



egg cells. The reproductive girdle, or clitellum, already spoken of, 

 forms the case which is to hold the eggs (see Fig. 71). When the 

 sperm cells have been exchanged, and the ova are ready for fertili- 

 zation, the worm draws itself backward from the collarlike case or 

 clitellum so that it slips over the head. As it passes the fifteenth 

 and sixteenth segments, it collects the ova, and as it passes the 

 ninth and tenth segments, it collects the sperm cells 

 previously received by touching another worm. The 

 elastic, collar-like clitellum closes at the ends after it 

 has slipped over the worm's head, forming a capsule. 

 The ova are fertilized in this capsule, and some of them 

 hatch into worms in a few days. These devour the 

 eggs which do not hatch. The eggs develop into 

 complete but very small worms before the worms 

 escape from the capsule. 



Habits. — The earthworm is omnivorous. It 

 will eat bits of meat as well as leaves and other 

 vegetation. It has also the advantage, when 

 digging its hole, of eating the earth which must 

 be excavated. Every one has noticed the fresh 

 "casts" piled up at the holes in the morning, fig. 78.— 



Side view 



As the holes are partly filled by rains, the showing setae, 

 casts are most abundant after rains. The 

 chief enemies of the earthworm are moles and 

 birds. The worms work at night and retire so 

 early in the morning that it takes a very early bird to catch 

 a worm. Perhaps the nearest to an intelligent act the 

 earthworm accomplishes is to conceal the month of its hole 

 by plugging it with a pebble or bit of leaf. They hiber- 

 nate, going below danger of frost in winter. In dry weather 

 they burrow several feet deep. 



The muscular coat beneath, and much thicker than the 

 skin, consists of two layers : an outer layer runs around the 

 body just beneath the skin, and an inner, thicker layer of 



nephridia 



pores, and 



reproductive 



openings. 



