. Elements of comparative zoology. Zoology. MOLLUSCS. 211 Order I.—Tetrabranchiata. In the Tetrabranchs there are two pairs of gills (, four in all); the head bears numerous short tentacles without suckers, and the body is enclosed in a chambered shell. The pearly nautilus is the only living representative of this. Fig. 46.—Female Nautilus, the shell laid open (from Ludwig's Leunis). 1, man- tle; 2, dorsal lobes; 3, tentacles; 4, head fold; 5, eye; 6, siphon; 8, shell muscle; 9, living-chamber; 10, partitions between chambers; 11, siphuncle. group. It occurs in the East Indian seas, and, w
. Elements of comparative zoology. Zoology. MOLLUSCS. 211 Order I.—Tetrabranchiata. In the Tetrabranchs there are two pairs of gills (, four in all); the head bears numerous short tentacles without suckers, and the body is enclosed in a chambered shell. The pearly nautilus is the only living representative of this. Fig. 46.—Female Nautilus, the shell laid open (from Ludwig's Leunis). 1, man- tle; 2, dorsal lobes; 3, tentacles; 4, head fold; 5, eye; 6, siphon; 8, shell muscle; 9, living-chamber; 10, partitions between chambers; 11, siphuncle. group. It occurs in the East Indian seas, and, while the shells are very common, the animal is very rare in museums. In geological times allied forms were very abundant, and are known as Ammonites (with tightly coiled shells), and Orthoceratites (with straight shells), etc. Order II.—Dibranchiata. These have two gills (one pair), and long, sucker-bearing arms. An ink-sac is always present. The order is sub- divided into the Octopoda, in which there are eight arms (fig. 47), and the Decapoda, in which the number is increased to ten by the addition of a pair of longer arms. In the Octopoda there is no internal shell, and the body. 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 Kingsley, J. S. (John Sterling), 1854-1929. New York, H. Holt and Company
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