Anatomy of Gorgonid.e. 151 



It may be well to add that cross sections ot the branch near 

 the tip reveal an investment of the axis which is composed of 

 cells closely resembling those forming the endodermal lining 

 of the calicle; and this investment is separated by considerable 

 mesodermal tissue from the water-vascular canals, as was the 

 case in Muricca. 



RHIPIDIGORGIA FLABELLUM. LINNA 

 ZoANTHODEME profusely branching; the branches disposed 

 in one plane and giving off numerous branchlets which anasto- 

 mose wherever they meet. This peculiarity results m the 

 flabellate zoanthodeme suggested by the specific name, as well 

 as by the popular name of sea-fan. The anastomosing of 

 the branchlets is carried out to the extent of producing a 

 reticulate structure. (See PI. X, fig. i). Ordinarily the main 

 stalks divide into several large branches which may be traced 

 to the periphery of the zoanthodeme as seen in the figure. 

 Sometimes, how^ever, the large branches break up, soon after 

 leaving the main stalk, into numerous anastomosing branchlets 

 which form an approximately uniform reticulation in which 

 the large branches are obliterated. The vertical branches, 

 however, are generally longer than the horizontal. The 

 greatest diameter of the branches is at right angles to the 

 plane of the zoanthodeme. 



The two surfaces of the fan differ in certain particulars. 

 The polyps are much more thickly implanted on one side than 

 on the other,'^ and the side on which there are fewer polyps 

 bears a number of short branchlets which are somewhat cla- 

 vate, curve outward and upward and occupy planes at right 

 angles to the general surface of the zoanthodome. 



Sometimes a smaller fan with its branches and reticulations 

 may spring from the main one to which it is attached by one 

 straight edge, its plane being at right angles to the parent 

 fan. 



1 Identified from memory by Dr. J. Walter Fewkes. 



2 This is usually but not always the case. 



