. Natural history. Zoology. ELEPHANT'S-TOOTH SHELLS, ETC. 629 18 probably taken by a double row of retractile filaments, each terminatin<. m a knob-like thickening, that encircle the base of the snout. The heart it quite rudimentary. The foot lies under the snout, and is a long, cylindrical body directed forwards and terminating in three lobes. The nervous system. V,-£^ Fig. IL- AO, Ailmentary canal. CO, Cephalic panfrlia. EA, Efferent aperture. -DENTALixfM Shell akd Diagram of Anatomy. F, Foot. M', Jlantle. S'. Shell. Liver. PG, Pedal ganglia. TT, TentJclee. M, Mouth. S, Snout YG, Visceral
. Natural history. Zoology. ELEPHANT'S-TOOTH SHELLS, ETC. 629 18 probably taken by a double row of retractile filaments, each terminatin<. m a knob-like thickening, that encircle the base of the snout. The heart it quite rudimentary. The foot lies under the snout, and is a long, cylindrical body directed forwards and terminating in three lobes. The nervous system. V,-£^ Fig. IL- AO, Ailmentary canal. CO, Cephalic panfrlia. EA, Efferent aperture. -DENTALixfM Shell akd Diagram of Anatomy. F, Foot. M', Jlantle. S'. Shell. Liver. PG, Pedal ganglia. TT, TentJclee. M, Mouth. S, Snout YG, Visceral ganglia. is simple and resembles in general arrangement that of the Pelecypoda already described (p. 620), except that the cerebral and pleural ganglia are not fused. The Scaphopoda live in mud, and feed on the small organisms they find in it. CLASS IV.—GASTROPODA. In this class are included mollusca like the snail, whelk, etc., that have a distinct head, and, along the underside of the body, a muscular foot on which they creep; whilst the visceral mass situated above is sometimes naked, but more often covered with a shell, composed of a single piece. The organs of the body are asymmetrical, , those on one side of the body are not matched by corresponding ones on the other. The shell is essentially a longer or shorter hollow cone. In some, such as the limpet, it is a simple cone, but in by far the greater number it is an elongated cone, coiled round and round spirally, each coil forming a whorl, the last being the body-ivhorl. Nearly all spiral shells are dcxtrul; that is to say, when placed with the mouth uppermost, and the apex directed away from the observer, the mouth lies to the right hand of the axis of the shell. Some are wound in the opposite direction, and are sinistral. Reversed varieties of shells normally dextral, or sinistral, are met with. The axis or cohimella of the shell is sometimes hollow or umhilicated (the hollow itself being called the umbilicus),
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Keywords: ., bookauthorly, bookcentury1800, bookdecade1890, booksubjectzoology
