. Cephalopoda. Cephalopoda. 56 Material for the studies on Nautilus was obtained from. Pacific islands, including a collection made by Professor Dahl in the 1890s from Ralum (Bismarck Archipelago), pther material, brought by a missionary to Europe and obtained by the station, at Naples, was rather abundant (about 20 speci- mens) and consisted of immature half-grown specimens which provided some data for embryonic development. The genital organs of the youngest forms, especially the oviduct and nidamental glands, were at a stage passed in Dibranchiata soon after hatching; the gland lamellae, fo
. Cephalopoda. Cephalopoda. 56 Material for the studies on Nautilus was obtained from. Pacific islands, including a collection made by Professor Dahl in the 1890s from Ralum (Bismarck Archipelago), pther material, brought by a missionary to Europe and obtained by the station, at Naples, was rather abundant (about 20 speci- mens) and consisted of immature half-grown specimens which provided some data for embryonic development. The genital organs of the youngest forms, especially the oviduct and nidamental glands, were at a stage passed in Dibranchiata soon after hatching; the gland lamellae, for example, were quite rudimentary and consisted of flat, ridge-shaped elevations (see Chapter 3). The material had been preserved for about 20 years in alcohol, and was not in ideal condition. However, this did not prevent determination of the major relationships, which is the object of this discussion. Jatta had already dissected some of the specimens, all of which were L. Results of the examination of this material will be published in detail elsewhere; this presentation will be confined to morphological elements, providing data for the determination of the typical cephalopod structure and allowing a comparison with the morphology of the Dibranchiata. As in all shell-bearing molluscs, the general habitus of the animal is largely determined by the shell which is well known. In recent species of Nautilu's tire shell may have a wide or narrow umbilicus or be without an umbilicus, and the last whorl of the shell in the mature animal may com- pletely envelop the preceding whorl (N. pompilius), or leave the axis of the coil free on each side (N. macromphalus and N. umbilicatus). The latter condition is undoubtedly the more primitive or typical, since it is also observed in young forms of N. p o m p il iu s. In the earliest parts of the shell, the coiling is even looser and the innermost whorl is completely evolute (Figure 9). The youngest stages of Nautilus have a horn-
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