COELENTERATA. 



Ill 



can always be distinguished. The mouth leads directly (Fig. 101, 

 Carmarina), or by a tube into the stomach, and its lips are often 

 drawn out into four grooved processes the oral arms (Fig. 100). 

 The edges of the grooves are often frilled, and carry small tentacular 

 filaments. 



In Rhizostoma the four arms bifurcate (Fig. 97), giving rise to eight, the frilled 

 edges of which fuse and bring about the closure of the mouth. The fusion is 

 not, however, complete, but numerous small openings are left the suctorial 

 monthlets, in which digestion 

 of the food takes place. From 

 these openings arise small ves- 

 sels, which gradually uniting 

 with each other form a system 

 of canals passing up the oral 

 arms to open into the stomach 

 (Fig. 97). 



The stomach is generally 

 flattened, rarely elongated 

 (Lucernaria, Periphylla, Tes- 

 sera) in its main axis. Occa- 

 sionally it is divided by a 

 constriction into two sections, 

 an aboral basal section and 

 a central stomach (Tessera, 

 Pericolpa, Periphylla (Fig. 99), 

 the stalk tube of Lucernaria). 

 Gastral filaments (phaceUae) 

 are highly characteristic of 

 the acraspedote medusae, and 

 recall the same structures in 

 the Anthozoa, as do the gas- 

 tral ridges or taenioles, which 

 to the number of four are 

 placed interradially in the 

 basal and central stomach in 

 the Lucernaridae and Tcsseri- 

 dae (Figs. 98, 99). 



en 



m se. 



FIG. 98. Section through the peripheral part of the 

 umbrella of a young Lucernarian (Crateroloplm* 

 thetys). ek ectoderm ; mes jelly ; en endoderm ; </ 

 central stomach ; rj' radial diverticula of the stomach 

 between the funnels (subgenital pits) ; g.t radial 

 pouches; se septa ; inf funnels lined by ectoderm; 

 m.se septal muscles ; m.i longitudinal muscles of the 

 funnels ; gen gonads (after Glaus). 



The peripheral part of 

 the gastrovascular system 

 may appear in the young 



form as a continuous dorso-ventrally flattened space extending 

 almost to the edge of the umbrella. Later the dorsal and ventral 

 walls of this space come together along certain radially directed lines 

 and fuse with one another, so that the originally continuous space is 

 broken up into a number of pouches or vessels, all leading outwards 

 from the central stomach. At the places where the concrescence of 



