. Buccinum : (the whelk). Buccinidae. 8 of papillae which give the shell the appearance of being covered with a velvety tissue. These papillae are all directed backwards towards the apex of the shell. In sections (Text-fig. 2) the periostracum appears to be made up of layers lying obliquely to the surface. A spine is simply a prolongation of one of these layers. The outer layer (a) of shell (Text-fig. 2, a) is marked by the possession of more organic substance than the other layers. The calcareous substance crystallises irregularly as mentioned above, and the appearance can be understood bette
. Buccinum : (the whelk). Buccinidae. 8 of papillae which give the shell the appearance of being covered with a velvety tissue. These papillae are all directed backwards towards the apex of the shell. In sections (Text-fig. 2) the periostracum appears to be made up of layers lying obliquely to the surface. A spine is simply a prolongation of one of these layers. The outer layer (a) of shell (Text-fig. 2, a) is marked by the possession of more organic substance than the other layers. The calcareous substance crystallises irregularly as mentioned above, and the appearance can be understood better perhaps from the photograph (PI. I, fig. 6) than from any description. The middle layer, Text-fig. 2 (6), is, as we have seen above, marked in longitudinal sections by parallel lines running perpendicular to the surface of the shell. In transverse sections, however, the appearance of this layer. Fig. 2. is, as Tullberg remarked, just like the inner layer (c) in longitudinal section. This structure will be understood better when the remaining two layers (c and d) inside it are examined in transverse section. It will then be seen that the layer (d) is marked like the middle layer (b), and thus both (b) and (d) seem built of parallel columns in longitudinal sections, whilst they are marked by oblique lines in transverse section. The layer (c) is apparently built up of parallel columns in transverse section. The reason for this strange appearance is that the three inner layers (b, c, and d) are built up in exactly the same way. 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 Dakin, William J. (William John), 1883-1950. London : Williams & Norgate
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Keywords: ., bookcentury1900, bookdecade1910, bookpublisherlondo, bookyear1912
