. Zoology : for students and general readers . Zoology. 230 ZOOLOGY. etc., as well as over the ground, by minute, short, curved setffi 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 (cceca), and the intestine, which is externally tubular, contains a thick inter- nal sac-like fold called a typhlosole. The segmental organs are highly convoluted tubes, a pair to each segment of the body, except a few near the head, and opening
. Zoology : for students and general readers . Zoology. 230 ZOOLOGY. etc., as well as over the ground, by minute, short, curved setffi 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 (cceca), and the intestine, which is externally tubular, contains a thick inter- nal sac-like fold called a typhlosole. 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 moncecious (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 {receptactila seminis). Pairing is reciprocal (see Fig. 151), each worm fertilizing the eggs of the other; they pair in June and July in tlie night-time. The eggs of the European Lumbriciis rtibellus Grube are laid in dung, a single egg in a capsule; L. agricola 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- Fiff. 151.—Earth-worms pairing;. After Curlie. ^ i . a, embryo (blastula) soon after segmentation of truia and neurula stage, tbe yolk : ^, embryo further advanced; 0, month; .-. i i i i f, embryo Btill older; *, primitive streak ; d, the WOrm, WhCU hatCll- neurala ; o, its 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 gardens and ploughed. Please note
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1879
