iv PHYLUM CCELENTERATA 187 



the fourth twenty, and the fifth or outermost forty, making a total 

 of eighty. 



Obviously the Sea-anemone is a polype, formed on the same 

 general lines as a Hydra or a scyphula, but differing from them in 

 having numerous tentacles arranged in multiples of five, and in 

 the absence of a hypostome, the mouth being nearly flush with the 

 surface of the disc. Its great size and bulk, and the comparative 

 firmness of its substance, are also striking points of difference 

 between Tealia and the polypes belonging to the classes Hydrozoa 

 and Scyphozoa. 



Enteric System. — Still more fundamental differences are found 

 when we come to consider the internal structure. The mouth does 

 not lead at once into a spacious undivided enteric cavity, but into 

 a short tube (gul.), having the form of a flattened cylinder, which 

 hangs downwards into the interior of the body, and terminates in 

 a free edge, produced at each end of the long diameter into a 

 descending lobe or lappet (lp.). This tube is the gullet or stomodceum, 

 a structure we have already met with in the Scyphozoa, but which 

 here attains a far greater size and importance. Its inner surface is 

 marked with two longitudinal grooves (A and B, sgph.), placed one 

 at each end of the long diameter, and therefore corresponding with 

 the lappets : they are known as the gullet-grooves or siphonoglyphes. 



The gullet does not simply hang freely in the enteric cavity, 

 but is connected with the body-wall by a number of radiating 

 partitions, the complete or primary mesenteries (mes. 1) : between 

 these are incomplete secondary mesenteries {mes. 2), which extend 

 only part of the way from the body-wall to the gullet, and 

 tertiary mesenteries {mes. 3), which are hardly more than 

 ridges on the inner surface of the body-wall. Thus the entire 

 internal cavity of a Sea-anemone is divisible into three regions : 

 (1) the gullet or stomodaum, communicating with the exterior 

 by the mouth, and opening below into (2) a single main digestive 

 cavity, the stomach or mescnteron, which gives off (3) a number of 

 radially arranged cavities, the inter -mesenteric chambers or metentera. 

 It is obvious that we may compare the gullet and stomaSh with 

 the similarly named structures in the scyphu la-stage of Aurelia, 

 and the mesenteries with the gastric ridges ; indeed, there seems to 

 be little doubt that these structures are severally homologous. A 

 further correspondence is furnished by the presence of an aperture 

 or ostium (ost. 1) in each mesentery, placing the adjacent inter- 

 mesenteric chambers in direct communication with one another : 

 in Tealia a second ostium (ost. 2) is present near the outer edge 

 of the mesentery. Moreover, the free edge of the mesentery 

 below the gullet is produced into a curious twisted cord, the 

 mesenteric filament (mes. /.), answering to a gastric filament of 

 the Scyphozoa. In many Sea-Anemones the mesenteric filaments 



