20 BRITISH FOSSIL CORALS. 



The ridges which mark the lips are continued on to this vacant space, and radiate 

 towards the bases of the tentacules. 



In some species the moveable mouth and the hollow between it and the tentacules are 

 of more use in obtaining food than the tentacules themselves.^ 



The contrary is very evident in Caryo^jhyllia davus" (the CaryophylUa borealis of British 

 zoophytologists), and in Cladocora casjntosa? In these species the tentacules are greatly 

 developed and extend close up to the base of the cone which is surmounted by the mouth 

 and lips ; there is but little of the disc unoccupied, and the power of protrusion on the 

 part of the cone is comparatively slight. Yet it must be observed that when the tentacules 

 are withdrawn, the mouth is capable of being projected further than Avhen they are in full 

 extension. 



The lips, the external surface of the cone, and the disc, are covered with cilia. At the 

 marginal extremity of the disc in some species, and scattered over more or less of the 

 whole disc and extending even very close to the labial orifice, in others, are the tentacules.* 

 These organs vary in length and thickness in different species, but each has a base con- 

 tinuous with the tissues of the disc and opening into the upper part of the visceral cavity. 

 Generally terminated by a bulbous swelUng, the tentacules are perforated throughout by a 

 delicate canal, and consist of tissues which render them very mobile, contractile, extensile, 

 and more or less prehensile. The external margin of the disc corresponds with the 

 calicular margin ; it is separated from it by a very small space, is continuous with the 

 tissues covering the outside of the coral, and in some species has a small fold which 

 covers in the tentacules. 



The opening of the mouth, when fully expanded, admits of the columellary surface 

 being seen at the bottom of a shallow cavity ; and the sides of this cavity, marked by the 

 continuation of the ridges noticed on the lips and disc, are often protruded through 

 the lips.^ The cavity is the stomach, and it is separated from the visceral cavity, which 

 is below or at about the level of a prominent columella, by a faint constriction — the 

 pylorus. The stomach is very short and very extensile. 



The sides of the cavity are continuous, by means of the lips, with the outside of 

 the disc ; they are formed by the same tissues, but the tegumentary layer of the 

 disc is altered and becomes the superficial layer of the mucous membrane of the 

 stomach. 



The ridges already noticed on the hps, disc, and stomach, correspond on the under 

 side of the disc and outside of the stomach with mesenteric folds. 



The pylorus opens into the visceral cavity, whose upper boundary is the lower surface 

 of the tentaculiferous disc, and it therefore is clear that the stomachal membranes con- 



1 Plate II, fig. 10. 2 Plate II, figs. 7—11. ^ Plate II, fig. 4. 



* Plate II, figs. 4, 7, 11, 12, 13, 14, 17, 18, 19, 20. 

 ' The ridges are seen in Plate II, figs. 11, 13, 14. 



