FORM REGULATION IN CERIANTHUS. 



269 



FIG. i. 



According to this view there' is an inward and an outward 

 current in the stomodaeum and for a greater or less distance 

 aboral to it in the central region of the enteron between the mar- 

 gins of the mesenteries. According to my own observations con- 

 ditions are very similar in Ccriantlnts. Only one siphonoglyphe 

 is present (Fig. i) and along this the current is directed in- 

 ward, though whether the cilia may ever re- 

 verse this movement has not determined. The 

 fact that small particles placed on the disc, if 

 not ingested by muscular action, are gradually 

 carried in a peripheral direction indicates that 

 here the cilia beat so as to cause an outward 

 current. The direction of the current on the 

 lower parts of the oesophagus outside of the 

 siphonoglyphe has not been determined, but is probably the same 

 as upon the disc and upper portions. In Fig. 2 the opposing 

 stomodaeal currents are indicated by arrows, the inward current 

 along the siphonoglyphe by the longer arrow on 

 the left and the outer currents by two shorter 

 arrows on the right. 



The natural conclusion is that the accumulation 

 of water in the enteron is in some way the result- 

 ant of the stomodaeal currents, but the manner in 

 which this result is attained requires consideration. 

 When the enteron is distended with water under 

 pressure the walls of the oesophagus must be 

 brought into contact since pressure is exerted 

 upon them from all sides by the water in the 

 enteron. The radiating grooves corresponding 

 to the lines of attachment of the mesenteries, which 

 are visible upon the disc of Ccrianthns, extend the 

 whole length of the stomodaeum and probably it 

 is along these that the chief outward currents pass. 

 As the walls of the oesophagus are pressed more 

 more closely together these grooves are more and more nearly 

 obliterated. Probably when internal pressure is high the out- 

 ward currents are very slight or absent. The siphonoglyphe, 

 however, is a relatively powerful organ, which produces an in- 



FIG. 2. 



