17 



iluis inhaled is diiveii Ly vortices created by tlie cilia of 

 the endoderm into the canals of the mesogloea, and thus 

 the rapidly growing parts of the colony are supplied with 

 oxygenated water. The remainder travels down the 

 ventral sides of the coelenteric cavities. A current of 

 water in the opposite direction is produced by the cilia 

 of the long dorsal mesenterial filaments (see Plate III., 

 tig. 20 Driif.) which, probably makes its exit by way of the 

 dorsal side of the stomodaeum. In this manner a regular 

 circulation of the water in the colony is maintained 

 during the time when the polyps are expanded. 



UiGESTiox. — Particles of food which are caught by the 

 tentacles are, if suitable in size, passed to the mouth and 

 rapidly swallowed by the stomodaeum. The stomodaeum 

 in Alcyouium is not, as it is in Xenia, and some other 

 Alcvonarians, a digestive tube. The food is unaltered 

 during its passage through it. On passing the lower or 

 inner opening of the stomodaeum the six ventral mesen- 

 terial filaments embrace it, and hold it fast for some time. 

 During this time the glands on these mesenterial fila-- 

 ments secrete a digestive fluid, which partly dissolves it 

 and breaks it up. The food which is thus dissolved is 

 assimilated by the general endoderm lining the coelen- 

 teron, and possibly also by the ventral mesenterial fila- 

 ments themselves. Food particles that escape from the 

 embrace of the mesenterial filaments and particles of oil 

 or fat which are not dissolved by the digestive ferment 

 are swallowed by endoderm cells and digested intra- 

 cellularly. The ferment of the digestive fluid secreted 

 by the filaments is alkaline in most Coelenterates, and 

 the ferment secreted by the endoderm cells into their 

 food vacuoles is an acid ferment. From the few observa- 

 tions that have been made on Alcyouium, it is probable 

 that in this respect it agrees with other Anthozoa. 



