422 H. BOSCHMA. 



In other groups of Anthozoa there are also a number of state- 

 ments on the digestive function of the mesenterial filaments. In 

 Pennatula and Virgularia Marshall and Marshall (1882) found 

 foreign bodies embedded in the cells of these organs. Wilson 

 (1883) has observed the ingestion of food by the mesenterial 

 filaments of Leptogorgia, and the same author found diatoms and 

 other solid foreign corpuscles enclosed in the mesenterial filaments 

 of alcyonid polyps (Wilson, 1884). The most elaborate researches 

 on digestion in octactinians have been made on Alcyonium. 

 According to Hickson (1901) the mesenterial filaments of this 

 animal secrete a digestive fluid which dissolves the food. The 

 latter is afterwards ingested by the entoderm of the gastric cavity. 

 These conclusions were confirmed by Pratt (1906). After elabo- 

 rate feeding experiments on Alcyonium and the study of the 

 changes in histological structure before and after feeding in the 

 polyps of this form Pratt came to the same conclusion: in 

 alcyonid polyps extracellular as well as intracellular digestion 

 occurs. Before feeding the gland cells in the stomodseum and in 

 the mesenterial filaments are filled with a secretion, after feeding 

 they are empty. Pratt concludes that this secretion is mixed 

 with the food in the gastric cavity and causes the partial disso- 

 lution of the larger objects. Afterwards the small particles are 

 ingested by the cells of the mesenterial filaments. 



The opinion of Dantan (1921) that the digestion of antipa- 

 tharian polyps is only extracellular is solely based on the histo- 

 logical study of the one polyp in which food-particles could be 

 found. This observation does not give sufficient evidence for the 

 opinion that the polyps of this group are in respect to their 

 digestion quite different from all other anthozoans. 



In the mesenterial filaments of zoanthids also foreign bodies are 

 found embedded in the cells (McMurrich, 1889, 1899). The 

 zoanthid polyps therefore in all probability digest their food in the 

 same way as other anthozoans. 



As stated above, a great number of investigators found that the 

 mesenterial filaments are the chief organs of digestion in antho- 

 zoans. In many of these statements the accurate place of the 

 ingestion is said to be the part immediately behind the marginal 

 zone which contains a great number of gland cells and nemato- 



