Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct : for the use of schools and colleges . Fig. 193.—The dental organ of Fig. 194.—The dental organ of a the Nerita Ascensionensis. Patella, from the Straits of Magellan. have solid jaws closely resembling the beak of a parrot(fig. 192), which move up and down, as in birds. [But a muchlarger number rasp their food by means of a tongue sometimescoiled like a watch-spring, the surface of which is coveredwith innumerable tooth-like points, as in the highly mag-nified portions of the
Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct : for the use of schools and colleges . Fig. 193.—The dental organ of Fig. 194.—The dental organ of a the Nerita Ascensionensis. Patella, from the Straits of Magellan. have solid jaws closely resembling the beak of a parrot(fig. 192), which move up and down, as in birds. [But a muchlarger number rasp their food by means of a tongue sometimescoiled like a watch-spring, the surface of which is coveredwith innumerable tooth-like points, as in the highly mag-nified portions of the dental organ of Nerita (fig. 193)and Patella (fig. 194). The teeth present a great varietyof patterns, which are constant in the different genera, andeven characterize the species. They consist of variously-co-loured silicious bodies, generally of hook-like forms, ar-ranged in triple rows upon a musculo-membranous band, ORGANS OF MASTICATION. 187 as in figs. 193 and 194. The central part is called therachis, and the lateral parts pleurce. The rachidian teethsometimes form a row of plates, as in Nerita ; or they havea tile-shaped disposition, with
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1870
