the role of mucus in corals

602 J. B. DUJffiDEN.

I t is manifest that ciliary activity is an important factor inthe physiological activities of actinian and coral polyps, par-ticularly in combination with mucus, as will be more fullydiscussed later. The exhalent currents produced therebyserve to waft or float away whatever inert particles accumu-late upon the disc, while the inhalent currents are of muchsignificance in ingestion. The cilia are shown to react locally,and only upon direct contact with the stimulating substance,that is, their activity is not dependent upon nervous impulses,either near or distant.

EXPERIMENTS WITH FAVIA.

For a study of the reactions and feeding activities ofcolonial corals a species of Favia was employed. The indi-vidual polyps are here about 8 mm. across, and the tentaclesare closely arranged at the margin of the disc, so that thoseof adjacent polyps intermingle on full expansion (fig. 6).Compared with those of Fungia the tentacles of Favia takea greater part in the activities of the polyp.

"When very light debr is is dropped upon a colony of Faviawith the polyps fully expanded, the lighter particles are caughtin the exhalent currents from the various stomodfea, while theheavier fall on the disc, and become embedded in the super-ficial layer of mucus. The free floating particles over any onepolyp are wafted rather quickly from the mouth towards thetentacular region, beyond which they seem about to pass, whenthey are immediately checked, in such a manner as to demon-strate that between the individual polyps there is either anapproximate neutral zone or one in which the current movesupwards (fig. 4).

The marginal regions, where the tentacles from adjacentpolyps intermingle, thus become occupied by particles drivento and fro within very narrow limits; sometimes the objectspass more over the disc of one polyp, and then further over anadjacent polyp. Ultimately, however, the particles come to