EARTH WORMS. 



61 



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



it also swallows tlu- dirt, which passes through the digestive 

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



feet ill the soil. 



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

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



bringing the Bllbsoil to the surface and allowing the air to 

 get to the root- 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 og^ in June and July, at night. 



Fio.W— Earth-worms, nat size, a, embryo (blastula) n after sejrmeni I 



oitneyolk; /.. embryo further advanced ; ... mouth; <-. embryo still older; k. 

 primitive str.uk; d, neurulajo, its mouth. 



The eggs of the European Lumbricus rubellus are laid in 

 dung, a single i gg in a capsule: /.. agricola lavs numerous 

 egg-capsules, each containing sometimes as many as fifty 

 . 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. thai the body is 



shorter and with a much less number of segments. 



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

 Clymenella (Fig. 07). which lives in tubes in soft mud. 



*Pun\ in s Formation of vegetable mould through the action of worms. 



