FEEDING REACTIONS IN CORAL POLYPS. 421 



mesenterial filaments could be digested, and concluded that an 

 enzyme causing extracellular digestion can be secreted by the 

 mesenterial filaments. This opinion is also found in an article 

 by Willem (1916), who maintains that extracellular digestion of 

 the larger particles precedes the ingestion (phagocytosis) of the 

 small particles, which are further dissolved by intracellular 

 digestion. 



The opinion of Biedermann (1911) on this question is in some 

 respects an intermediate one between the two views dealt with 

 above: he supposes that besides the intracellular digestion also 

 the secretion of a digestive enzyme occurs. The reason why the 

 enzyme is not found free in the gastric cavity (Mesnil, 1901) is 

 according to Biedermann probably the following: only small 

 quantities of digestive fluid are secreted by the mesenterial fila- 

 ments, and only in immediate contact with the food. 



Jordan (1913) upholds his original opinion, based on experi- 

 ments with food packed in filter paper (Jordan, 19070), which was 

 digested in the gastric cavity of the polyps. This proves that the 

 enzyme can easily penetrate through the whole of the food corpus- 

 cles and diffuse through every part of the gastric cavity where 

 food particles are present. There is no special need for a contact 

 of the food with the mesenterial filaments. 



The principal organs of digestion in madreporarians are the 

 mesenterial filaments, the same as in actinians. In Ccenopsammia 

 (Dendrophyllia) Gardiner (1900) found a small crustacean in one 

 of the polyps, supported by the mesenterial filaments, which 

 indicates that it was being digested here. In the mesenterial 

 filaments of Flabellum the same author (Gardiner, 19040) found 

 fat globules and diatoms and other algal matter in the cells of the 

 portion next to the edge which is crowded with nematocysts. 

 When remains of partially digested food were found in the gastric 

 cavity of madreporian polyps, these were lying against the 

 mesenterial filaments, as recorded by Carpenter (1910) for 

 Isophyllia (Mussa) and by myself (1924) for Favia. Moreover 

 strong evidence for the digestive function of the mesenterial 

 filaments is given by Vaughan (1912), who states that these 

 organs in Orbicella may protrude through the column wall and 

 catch and digest the food outside the gastric cavity. 



