Anatomy of Gorgonid.^. hi 



are not grouped around the aggregation of spicules which 

 constitute the axis cylinder, but are somewhat evenly distribu- 

 ted throughout the coenenchyma, thus torming a large series 

 of canals running parallel to the axis of the branch. This 

 arrangement seems to approach that of the Alcyonidse, with 

 this important difference that the canals in the latter contain 

 continuations of the mesenteries of the polyps, traversing their 

 whole length.' 



The primary canals contain an external^ investment of basal 

 substance (mesodermal), and an internal lining of endothe- 

 lium' (endodermal). These endothehal cells are quadrate in 

 form, and an examination of a living specimen will show that 

 they are ciliated. The ciliated cells are the cause of the rapid 

 flow of the water through the water-vascular system. They 

 thus serve the purpose of a heart, although it must be under- 

 stood that this is an analogical, and by no means a homologi- 

 cal resemblance. 



The primary canals send off numerous branches which 

 traverse the coenenchyma in every direction, anastomosing 

 freely. These branches seem also to be lined with endothelial 

 cells and often serve to connect the polyps directly with the 

 main canals. 



Secondary Water-vascular Canals. These may be termed 

 the capillaries of the water-vascular system. Indeed the 

 more one studies these vessels the more he is struck wath 

 their close resemblance to the real capillaries of vertebrated 

 animals. These vessels are usually minute in size, and are 

 found throughout the coenenchyma of this species. They 

 occur rather sparingly in the region of the spicular axis in 

 the centre of each branch, and are more profusely distributed 



1. Ces cloisons alternent avec les tentacules, les cavites qu'elles limitent se 

 continuent done supei'i^urement dans ceux-la. Inferieurement elles s'ouvrent 

 toutes dans la cavite g^n^rale du poljpe, qui plonge jusque dans la profondeur 

 du zoanthodeme. Pouchet et Mydvre. Contribution a I'Anatomie des Alcy- 

 onaires, p. 287. 



2. External from axis of canal. 



3. See PI. I, fig. II. 



