. Outlines of zoology. Zoology. ARENICOLA. 195 surface. This work, comparable to that of earthworms, tends to cleanse the sand and to reduce it to a finer powder. When getting rid of the casting, the worm lies with its tail upwards and its head downwards, or with its body bent like a bow; when the tide comes in, the mouth may protrude at the other end of the U-shaped tube. The worms that live between tide-marks seem to differ in many respects (as to colour, gills, habits, and sexual maturity) from those which occur in the Laminarian zone, which is only un- covered at low spring-tides. Ehlers s
. Outlines of zoology. Zoology. ARENICOLA. 195 surface. This work, comparable to that of earthworms, tends to cleanse the sand and to reduce it to a finer powder. When getting rid of the casting, the worm lies with its tail upwards and its head downwards, or with its body bent like a bow; when the tide comes in, the mouth may protrude at the other end of the U-shaped tube. The worms that live between tide-marks seem to differ in many respects (as to colour, gills, habits, and sexual maturity) from those which occur in the Laminarian zone, which is only un- covered at low spring-tides. Ehlers states that at certain seasons the adults swim about freely, but this requires corroboration. The young stages are for a time pelagic. External appearance.—The lob-worm varies in length. Fig. 85.—Arenicola marina. Entire animal viewed slightly from left side. _ Note anterior mouth ; setae on anterior region; setae and gills on median region; thinner tail region often longer than shown. from 8 in. to a foot, and at its thickest part is about half an inch in diameter. There are three regions in the body:—(a) The anterior seven segments, of which all but the first have bristles; (b) the middle region of thirteen segments, with both gills and bristles; (c) the thinner posterior part of variable length, without either gills or bristles, and with an inconstant number of segments (up to about thirty). In the very front there is a head-lobe or prostomium, but there are no tentacles or eyes. Anteriorly a soft proboscis is often protruded from the gut. The anus is terminal. Skin, muscles, and appendages.—Each segment is marked by about four superficial rings. The epidermis is pigmented and secretes mucus, and is divided into. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Thomson, J. Arthur (John Arthur), 1861
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Keywords: ., bookauthorth, bookcentury1800, bookdecade1890, booksubjectzoology
