The physiology of the circulation in plants : in the lower animals, and in man : being a course of lectures delivered at surgeons' hall to the president, fellows, etc of the Royal college of surgeons of Edinburgh, in the summer of 1872 . tractedat pleasure (Fjg. 122). In the garden-snail (Helix pomatia), thetentacles are hollow tubes, composed of circular bands of each tentacle is a long muscular slip (Fig. 123, c, d), extend-ing between its free extremity and the common retractive musclesof the foot. When the muscular slip (c) shortens, the circularmuscular fibres elongate, and
The physiology of the circulation in plants : in the lower animals, and in man : being a course of lectures delivered at surgeons' hall to the president, fellows, etc of the Royal college of surgeons of Edinburgh, in the summer of 1872 . tractedat pleasure (Fjg. 122). In the garden-snail (Helix pomatia), thetentacles are hollow tubes, composed of circular bands of each tentacle is a long muscular slip (Fig. 123, c, d), extend-ing between its free extremity and the common retractive musclesof the foot. When the muscular slip (c) shortens, the circularmuscular fibres elongate, and the tentacle is invaginated (a). Thesame thing happens in invagination of the intestine. A reverseaction takes place when the tentacle is protruded (b), the enclosedmuscular slip (cl) elongating, and the circular fibres the evagination or protrusion of the tentacle is not due tothe contraction or shortening of the circular fibres alone, is evidentfrom this. If the tentacle is half invaginated (a), the shorteningor closing of the circular fibres by themselves tend rather toinvagination than evagination. To complete the process, thelongitudinal muscular slip (c) must elongate, and push slightly. Fiff. 122. Fis. Fig. 122 shows tentacles of murex (a, b) in elongated state.—Adapted. Fig. 123 shows the four tentacles of garden-snail (a, b, «,/); one of which (a) is invaginated,and its muscle (c) shortened; a second one (b) heing evaginated or pushed out, and its muscle(d) elongated.—Adapted. When a garden-snail elongates its tentacles, we feel that theact is a voluntary and a vital one. The moment, however, they 2b 188 DR J. BELL PETTIGREW ON THE touch a foreign body, they The alarm passes away, andagain the tentacles are cautiously elongated. The same thinghappens in the sea-anemone. When this magnificent creatureexpands its tentacles like a gorgeous flower opening to thesunlight, it pushes them out with exquisite grace like so manymicroscopic tel
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