230 



ZOOLOGY. 



etc., as well as over the ground, by minute, short, curved 

 setae or bristles, which are deeply inserted in the muscular 

 walls of the body, and arranged in four rows along each side 

 of the body. The alimentary canal is straight, the stomach 

 has three pairs of small lateral blind sacs (coeca), and the 

 intestine, which is externally tubular, contains a thick inter- 

 nal sac-like fold called a typlilosole. 



The segmental organs are highly convoluted tubes, a pair 

 to each segment of the body, except a few near the head, 

 and opening internally with ciliated funnels and externally 

 in minute pores situated along the under side of the body. 

 The earth-worm is monoecious (hermaphroditic). 



The oviducts open in the fourteenth segment, and the 

 seminal ducts (vasa deferenfia) in the fifteenth. Between 

 the ninth and tenth, and the tenth and eleventh segments 

 are the four openings of the seminal receptacles (receptacula 

 seminis}. Pairing is reciprocal (see Fig. 151), each worm 

 fertilizing the eggs of the other ; they pair in June and July 

 in the night-time. The eggs of the European Lumbricus 



rubellus Grube are laid 

 in dung, a single egg in 

 a capsule ; L. ayricola 

 lays numerous egg-cap- 

 sules, each containing 

 sometimes as many as 

 fifty eggs, though only 

 three or four live to de- 

 velop. The development 

 of the earth-worm is like 

 that of the leech, the 

 germ passing through a 



morula (blastula), gas- 

 Fig. 151. -Earth-worms pairing. After Curtis. 



, embryo (blastula) soon after segmentation of trula and lieurula Stage, 

 the yolk ; 6, embryo further advanced ; 0, mouth ; , , , 



c, embryo still older ; k, primitive streak ; d, the WOrm, When hatch- 

 ing, resembling the pa- 

 rent, except that the body is shorter and with a much less 

 number of segments. 



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

 their habit of boring in the soil of gardens and ploughed 



a 



