Anatomy of Gorgonid^. 119 



polyps. The lining (endodermal) of the calicles is continuous 

 with that of the secondary water-vascular canals, and the 

 latter with that of the primary canals, so that both systems 

 are lined with endothelium. 



The circulation through the canals is further aided by the 

 cilia that are profusely distributed over the surfaces of the 

 organs within the general body cavity of the polyps. Ex- 

 amination of the fresh specimens reveals the fact that the calic- 

 ular lining, the gastric or mesenterial filaments, and even the 

 surfaces of the ova and planulte, are all densely ciliated and 

 produce active movements of the water within the calicles. 

 In connection with this the fact that the external surfaces of 

 the tentacles are also ciliated, is of interest, showing as it does 

 the efficient manner in which every part, external and inter- 

 nal, of the polyps is constantly bathed in currents of fresh sea- 

 water. Nothing could be more complete and thorough than 

 the means by which this is effected. 



Capillaries. By this term I designate the ultimate ramifi- 

 cations of the water-vascular system. These are minute 

 tubes formed by mesodermal cells which penetrate through 

 every part of the zoanthodeme except the axis cx'linder. 

 They present the appearance of transparent vessels with walls 

 dotted with nuclei, and are even more tortuous in their course 

 than the secondary canals with which they communicate 

 freely. 



It is somewhat difficult to homologize satisfactorily the 

 water-vascular system here described with that of Briareum. 

 Perhaps as satisfactory a statement as any would be as fol- 

 lows: 



I St. Bt'iarcum has no homologue of the primary canals of 

 Plexaurella. 



2d. The canals which I have called ■primary in Briareum^ 

 are hotnologically equivalent to the secondary canals of Plex- 

 aurella. 



3d. The secondary canals of Briareum are equivalent to 

 the capillaries of Plexaurella. 



