1. Whereas in Lamellibranchia a crystalline style is very common, in Gastropoda it occurs in it few genera only.
2. Crepidula possesses a crystalline style contained in a sac which is partially differentiated from the intestine, being separated therefrom by dorsal and ventral typhlosoles.
The stomach hears a gastric shield and a peculiar groove which is the continuation of the oesophagus. The head of the style lies in the anterior part of the stomach and impinges on the gastric shield.
3. The epithelium of the style-sac consists of densely ciliated cells of moderate length in which the internal rootlets of the cilia extend through the length of the cell and become greatly thickened at the base. The epithelium is specially characterized by the presence of an ‘intra-epithelial’ network of canals containing numerous fibres whose function is probably a mechanical one. The same structures are present, though less prominent in the epithelium of the typhlosoles, the cells of which are longer and narrower than those of the style-sac epithelium.
4. The crystalline style is a straight transparent rod of gelatinous consistency. It is built up of co-axial layers surrounding a spiral core. It is composed principally of globulin and contains an amylolytic enzyme.
Food is brought to the stomach embedded in a stream of mucus which becomes entangled with the head of the style. The function of the style appears to be to mix together the contents of the stomach and to supply a starch-splitting enzyme.
5. The crystalline style and style-bearing region of Crepidula resemble in great detail those of certain Lamellibranchs in respect of the shape, proportions, and structure of the style sac, typhlosoles, and intestine, of the presence of a gastric shield and of the form, composition, and function of the style.
6. The crystalline style in Gastropods may be classified under the same three types as are distinguished in Lamellibranchs in respect of the relations between the style-sac and intestine.
A list of Gastropods is given in which a style is known to occur, and a brief account is given of the various forms assumed by the style and style-sac in this class.
7. The crystalline style of Crepidula resembles that of Lamellibranchs in such detail that this organ must be regarded as strictly homologous in the two groups. It is to be supposed either that it has been lost in all but a few Gastropods, or that its appearance in this group is to be explained on the principle of orthogenesis.
8. In view of the fact that the food of Crepidula is identical with that of the oyster, the retention or appearance of a style in certain Gastropods might be correlated with the feeding habits. Investigations in this direction, however, have not met with very definite results.