A guide to the fossil invertebrate animals in the Department of geology and palaeontology in the British museum (Natural history) ... / With 7 plates and 96 textfigures.
- British Museum (Natural History). Department of Geology
- Date:
- 1911
Licence: In copyright
Credit: A guide to the fossil invertebrate animals in the Department of geology and palaeontology in the British museum (Natural history) ... / With 7 plates and 96 textfigures. Source: Wellcome Collection.
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![active predatory animals, or wliether they were sedentaiy and possibly attached by the shell, is uncertain. l>nt ceitain it is that at an early period the hump was drawn out into a lon<T visceral cone, and that the shell ac(]^uired a similar shape. Then followed a mode of growth very common in sedentary animals that form a tubular shell, and already observed in corals, worms, bryozoans, and gastropods. The mollusc continued to build up the shell around its opening, and thus formed a long tube. As the animal moved along this tube, the visceral cone was pulled away from the shell- Fig. 79.—Primitive Cephalopod shells: Endoccras. a, The end of a shell, broken at its apex; b, the same cut in half showing the chambers (sc), the swollen end of the wide neck-tube (cc), and calcareous substance deposited by the end of the siphuncle (cd). c. Fragment of another shell cut in half, showing the chambers separated by septa (.s), the largo neck-tube (sc), a sheath (sh), and the endosiphou (cn). Natural size, (a, b, after Holm; c, after Foord.) wall; but its skin went on secreting shell-substance, and formed a partition shutting off the space between the visceral cone and the outer wall. In Endoceras, here shown (Fig. 79), the visceral cone remained attached to the end of the outer shell, and shrank at a little distance from the apex, so that the partition or septum does not go right across the shell, but shuts off a chamber at the side. Shrinkage then took place a little higher up, and another chamber was formed. By the continuation of this process there arose a series of chambers entirely shut off by septa, and the down-turned portions or necks of these septa formed a long tube in which Gallery VII.](https://iiif.wellcomecollection.org/image/b24863841_0175.jp2/full/800%2C/0/default.jpg)
