Memoirs: The Rôle of Mucus in Corals

1. Under ordinary conditions the outer surface of coral polyps is covered with a thin, continuous layer of mucus, in which objects falling upon the polyp become embedded or entangled. 2. When first exuded the mucus is thin and watery, but later becomes more consistent. From time to time it is broken up into shreds and patches which are driven or wafted from the surface of the disc by the ordinary exhalent currents from the stomodaeum, along with any embedded foreign particles in it. 3. Nutritive substances and extractives placed upon the polyp increase the amount of mucus exuded, and also result iu an opening of the mouth and the institution of an inhalent stomodaeal current by reversing the dominant outward beat of the stomodtaeal cilia. 4. The mucus exuded as a result of nutritive stimuli is drawn down the stomodaeum by inhalent currents in the form of distinct streams, and carries with it whatever substances, nutritive or non-nutritive, are embedded or entangled in it. 5. Ingestion in coral polyps is thus purely mechanical, depending upon whatever substances are capable of producing an inward beat of the cilia, the opening of the mouth, and the exudation of mucus. Au inhalent current being established, objects are carried into the polypal cavity without regard to their nutritive value, and independently of any peristaltic motions on the part of the stomodasum. 6. In the ordinary activities of coral polyps inhalent currents may be occasionally instituted independently of any external stimuli, and these carry with them any inert objects resting upon the disc. 7. Mucus is of much importance in the protection of the polypal surface from foreign objects and in keeping it clean, and also in the entanglement and ingestion of prey and food substances.