Outlines of zoology . ormfrom its hole. As each of the four longitudinal rows is double, thereare obviously eight bristles to each ring. On the skin of the ventral EARTHWORM. 213 surface there are not a few special apertures, be looked for on a full-grown worm ; but careful examination of several specimens is usually necessary. Almost always plain on the 15th ring are the two swollen lips of the male ducts, less dibtinct on the 14th are the apertures of the oviducts through which the eggs pass, while on each side, between segments 9 and 10, 10 and II, are the openings of two recep
Outlines of zoology . ormfrom its hole. As each of the four longitudinal rows is double, thereare obviously eight bristles to each ring. On the skin of the ventral EARTHWORM. 213 surface there are not a few special apertures, be looked for on a full-grown worm ; but careful examination of several specimens is usually necessary. Almost always plain on the 15th ring are the two swollen lips of the male ducts, less dibtinct on the 14th are the apertures of the oviducts through which the eggs pass, while on each side, between segments 9 and 10, 10 and II, are the openings of two receptacula seminis or spermathecse into which male elements from another earthworm pass, and from which they again pass out to fertilise the eggs of the earthworm when these are laid. Each segment contains a pair of excretory tubes, which have minute ventral-lateral apertures, while on the middle line of the back, between the rings, there are minute pores, through which fluid from the body cavity may exude on to the Fig. III.—Anterior region ofearthworm.—After Hering. Skin and bristles. The Note the eight sets (j.) on each segment. , bpots between g-io, 10- 11,indicate openings of receptaculaseminis; Ovd., openings of oviductson segment 14 ; vd., openings of vasadeferentia on segment 15. thin cuticle is produced bythe cells which lie beneath,and is perforated by the aper-tures previously epidermis clothing the worm is a single layer of cells,of which most are simply supporting or covering elements,while many are slightly modified, as glandular or mucouscells, and as nervous cells. As the latter are connectedwith afferent fibres which enter the nerve-cord, the skin isdiffusely sensitive. In a few species the skin is slightlyphosphorescent. The chitinous bristles, which are longeston the genital segments, are much curved, and lie in smallsacs of the skin, in which they can be replaced afterbreakage. Muscular system and body cavity. — The earthwormmoves
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Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
