EARTH-WORMS. 



51 



swell out, and thus push the earth away on all sides, while 

 it also swallows the dirt, which passes tlirough the digestive 

 canal. In this way it may descend from three to eight 

 feet in the soil. 



While earth-worms are in the main beneficial, from their 

 habit of boring in the soil of gardens and ploughed lands, 

 bringing the subsoil to the surface and allowing the air to 

 get to the roots of plants, they occasionally injure young 

 seedling cabbage, lettuce, beets, etc., drawing them during 

 the night into their holes, or uprooting them.* 



Earth-worms lay their eggs in June and July, at night. 



Fig. S4.— Earth-worms, nat. size, a, embryo (blastula) soon after segmentation 

 of theyolli; 6, embryo further advancer! ; o, mouth; c, embryo still older; fc, 

 primitive streak; d, neurula;o, its mouth. 



The eggs of the European Lnmhrims rnlelhis are laid in 

 dung, a single egg in a capsule; L. agricola lays numerous 

 egg-capsules, each containing sometimes as many as fifty 

 eggs, though only three or four live to develop. The de- 

 velopment of the earth-worm is like that of the leech, the 

 germ passing though a number of stages, the worm, when 

 hatching, resembling the parent, except that the body is 

 shorter and with a much less number of segments. 



The sea-worms have larger, more distinct bristles, as in 

 Clymenella (Fig. 55), which livps in tubes in soft mud. 

 *Darwin's Formatiou of vegetable mould through the action of worms. 



