210 



ZOOLOGY. 



etc., as well as oyer the ground, by minvite, short, curved 

 setse 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 2:)airs of ^mall lateral blind sacs (coeca), and the 

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

 nal sac-like fold called a typMosole. 



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 th'e under side of the body. 

 The earth-worm is monoecious (hermaphroditic). 



The oviducts open in the fourteenth segment, and the 

 seminal ducts {vasa deferentia) 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. 145), each worm 

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

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



rubellus Grube are laid 

 in dung, a single egg in 

 a capsule ; L. ar/ricola 

 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- 



Kg. 145 .-Earth-worms pamng. After Curtis. ^ i , 



a, embryo (blastula) soon alter segmentation of trula and neuruia stagO, 

 the yolk ; 6, embryo further advanced ; 0, mouth ; ,, i n j_ i 



<;, embryo still older; *, primitive streak; d, tilC WOrm, When hatch- 

 neurulaio, its mouth-After Kowalevsky. ^^^^ 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 gai'dens and ploughed 



