42O H. BOSCHMA. 



the food takes place in actinians. The larger food-particles are 

 more or less dissolved into smaller corpuscles by the secretion of a 

 digestive fluid, and afterwards the small objects are ingested by 

 the entoderm-cells as described by Metschnikoff. The ingestion 

 of these small particles usually takes place in a zone of the 

 mesenterial filaments in the neighborhood of the free edge, but 

 after abundant feeding all the entoderm cells of the gastric cavity 

 can ingest food, even those of the acontia. In the sea-anemone 

 Tealia the soft parts of amphipods of the genus Talitrus are 

 completely dissolved till only the bare skeleton is left (Willem, 

 1892). In siphonophores Willem (1894) found approximately 

 the same phenomena: here also extracellular and intracellular 

 digestion are present. 



According to Chapeaux (1893) in the gastric cavity of actinians 

 a free digestive fluid can be demonstrated. The secretion of this 

 fluid occurs when food comes into contact with the mesenterial 

 filaments. When the food is ingested in the entoderm cells the 

 reactions of the food-vacuoles is acid. In siphonophores 

 Chapeaux found that 15-20 hours after ingestion of food colored 

 with litmus the vacuoles still had a red color. Chapeaux con- 

 cluded from this fact that the digestive enzymes of actinians and 

 siphonophores acted in an acid medium. The same opinion also 

 is upheld by Metschnikoff (1893), Mesnil (1909) and Roaf (1910). 

 On the other hand Jordan (19070) supposed that after the acid 

 reaction in the vacuoles an alkaline one would follow; the final 

 resorption of the food probably would take place in the latter 

 stage. The enzymes of the anthozoans then would present more 

 likeness to those of other groups of invertebrates, and act in about 

 the same way as the trypsin of vertebrates (cf. also Jordan, 

 19076). 



A number of investigations on digestion in actinians have been 

 made to show whether there is only intracellular digestion in these 

 animals or if there also is secreted a free digestive fluid which 

 dissolves the larger corpuscles into small particles which can be 

 ingested by the entoderm cells. According to Mesnil (1901) no 

 free enzyme is secreted in the gastric cavity: the digestion in 

 actinians is exclusively intracellular. Jordan (19070), however, 

 showed that food which could not come into contact with the 



