Anatomy of Gorgonid^. 147 



the primary water-vascular canals and the ectodermal invest- 

 ment of the zoanthodeme. 



In cross section these spicules show very plainly a concen- 

 tric laminate arrangement of the calcareous matter, which 

 seemingly indicates an exogenous mode of growth. The ap- 

 pearance is much like that of the lines of growth in a trans- 

 verse section of wood. Radiating lines also appear originat- 

 ing at what seems to be an axial cavity and sometimes forking 

 as they pass toward the periphery. 



2d. Much smaller fusiform tuberculate spicules like those 

 of Briareiim. These are purple in color and occupy a defi- 

 nite space around the axis cylinder, and between this and the 

 primary water-vascular canals. They are embedded in a soft 

 mesodermal sheath which surrounds the axis outside of its 

 endodermal investment, and are arranged with their long axes 

 parallel with the axis cylinder. The mesodermal sheath 

 spoken of does not appear to be firmly attached in alcoholic 

 specimens, to either the axis or primary canals. It can easily 

 be separated from both and removed for examination, when it 

 appears as a soft almost gelatinous mass of basal substance 

 in which are embedded a great number of pink or purple 

 spicules lying side by side so closely as almost to fill the mes- 

 odermal sheath. 



This latter is peculiar in its apparent lack of intimate con- 

 nection with associated structures, and in this respect presents 

 a character not observed in any other species. 



In cross sections many of these spicules exhibit a round 

 axial cavity. 



Similar tuberculate fusiform spicules which differ from 

 those around the axis chiefly in being colorless, are found 

 thickly implanted in the walls and tentacles of the polyps. As 

 they ascend the polyp walls they maintain a nearly uniform 

 size, being about as large as the spicules in the mesodermal 

 sheath around the axis cyHnder. As they mount upward in 

 the walls of the tentacles they rapidly diminish in size until 

 they become quite minute near the tips of the tentacles. They 



