. A manual of zoology. Zoology. Fig. 330.—Various forms of shells (after Schmarda, Bronn, and Clessin). A Patella costata; B, Haliotis tiibercutata; C,Lilhoglvphus natkoides; D, Vcrmetus denti- Jerus; E, shell of Murex opened to show c, columella; s, siphon. going first and then the metapodium, with its dorsal surface towards the aper- ture. Hence in many species this surface secretes a door, or operculum, which closes the aperture when the body retracts. Since the aperture increases in size with growth, the operculum enlarges in a spiral manner (fig. 330, C), some times forming a spiral line
. A manual of zoology. Zoology. Fig. 330.—Various forms of shells (after Schmarda, Bronn, and Clessin). A Patella costata; B, Haliotis tiibercutata; C,Lilhoglvphus natkoides; D, Vcrmetus denti- Jerus; E, shell of Murex opened to show c, columella; s, siphon. going first and then the metapodium, with its dorsal surface towards the aper- ture. Hence in many species this surface secretes a door, or operculum, which closes the aperture when the body retracts. Since the aperture increases in size with growth, the operculum enlarges in a spiral manner (fig. 330, C), some times forming a spiral line on the outside, or on both surfaces. Land snails are usually without opercula, but in hibernation they can close the shell by a calcareous plate, the epiphragm. In the spring this separates from the shell and is lost. In most gasteropods the shell is coiled to the right, but in some species (fig. 331) the whorls are constantly turned to the left, while reversed specimens occasionally occur in many species which are normally dextral. There are usually two layers in the shell, an inner lamellar layer (not always present), which sometimes is highly iridescent, and an outer opaque, porcellan-. 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 Hertwig, Richard, 1850-1937; Kingsley, J. S. (John Sterling), 1854-1929, ed. and tr. New York, H. Holt
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
