272 



C. M. CHILD. 



actinozoa is very evident from the frequent forcing out through 

 it of mesenterial filaments ; that it cannot be widely open during 

 distension of the body by water is equally evident. Doubtless 

 many differences in detail occur in different members of the 

 group, but it is probable that the suggestions given here for Ccri- 

 anthns vill apply more or less closely to a large number of forms. 

 The presence of two siphonoglyphes must condition certain mod- 

 ifications in these processes. The statement is made in several 

 text-books that the siphonoglyphes serve to keep the water in cir- 

 culation when the animal is contracted. According to the view 

 given above, these organs serve rather to permit circulation when 

 the body is distended. 



In addition to the inward and outward currents in the stomo- 

 dseal region the water in the intermesenterial chambers and in the 

 tentacles connected with them is in constant circulation, impelled 

 by the movement of cilia. I have not been able to determine the 

 details of this circulation in Ccrianthns, but have observed it in 

 several transparent members of the group. In general it may be 

 said that the current passes orally along the body-wall, periphe- 

 rally along the aboral face of the tentacle, back again along its 

 oral face, centrally beneath the disc, probably into and out of the 

 labial tentacles, to the stomodseum, and aborally along the sto- 

 modfeum. Whether cilia on the lateral surfaces of the mesenteries 

 aid in forcing the water aborally I clo not know. In the forms 

 observed, at any rate, the aboral current continued from the 

 aboral end of the stomodaeum to the aboral end of the body. 

 In all of the intermesenterial chambers are these circulatory cur- 

 rents. In Ccriantlnts itself they are difficult to demonstrate with 

 certainty, but there is little doubt that the current in the 'oral di- 

 rection along the body-wall exists, and this being present, we may 

 confidently assert that the return current is also present. These 

 currents in the intermesenterial chambers and tentacles may be 

 designated for convenience as the circulatory currents in distinc- 

 tion from the inward and outward currents of the stomodaeal 

 region. They are indicated diagrammatically by arrows in 

 Fig. 2. 



How far the circulation of water in the central regions of the 

 body is complicated by the complex arrangement of the mesen- 



