Considerations on phase‐change and decorations in snail shells

摘要

This paper, the third one in a series of investigations on snail shells, deals with various ontogenetic problems. In Lambis truncata no less than five phase-changes seem to take place during the development of the shell. In Murex each sector represents its own series of phase-changes, and, hence, the adult shell represents a long series of repetitions of the same shifts. In Conus, Turbo, Oliva and Cypraea a series of printing principles have been studied. Of these the “white spots” and the “dislocation” are of special interest and, as far as is known, have not been described previously. Both Oliva and Cypraea make the prints and stains from outside, whereas Conus and Turbo make the prints from inside and indirectly as an offset-printing. In Conus textile and in Oliva porphyria a dislocation of printed stripes occurs. This dislocation is evidently induced by different mechanisms (discussed in the text). In specimens of the Mauritia arabica group it was, surprisingly, established that the basal part of the shell is covered by a secondary epiostracum layer of the Cypraea tigris type, thus giving the shell the appearance of a chimaera. All these details are of genic origin, and result from activities of small, separate groups of genes. However, they are steps towards the genetically determined final result, a fully developed individual of a species with all its characters.