122 Natural History Bulletin. 



Mode of formation of the axis cylinder. I have been unable 

 to find the opinion of recent authorities on this matter. Pro- 

 fessor Huxley says, "It is in these OctocoraUa that the form 

 of skeleton which is termed sclerobase, which is formed by 

 cornification or calcification of the axial connective tissue of 

 the zoanthodeme, occurs." ' 



Balfour, on the contrary, says, " In the Actinozoa an epi- 

 blastic skeleton is exceptional, and according to most author- 

 ities absent. Quite recently however Koch has found that 

 the axial branched skeleton of most of the Gorgonid^, viz: 

 the Goro-QuincB and JsidincB, is separated from the coenosarc 

 by an epithelium, which he believes to be epiblastic, and to 

 which no doubt the axial skeleton owns its origin."'^ 



Colton, in his Practical Zoology, p. 175, says, "This horny 

 axis is excreted by the walls of these tubes." The tubes here 

 spoken of are the primary w iter-vascular canals. 



We have here a sufficient variety of opinions among authors 

 to show the difficulty of the subject. It seems to me quite 

 probable that each of the above opinions is incorrect, as I 

 have reason to believe that the axis cylinder is endodertnal in 

 origin. My reasons for this conclusion will be given at length 

 in connection with a description of Maricea on page 132. 



In regard to the species at present under consideration, I 

 think it probable that the horny core or medulla is homologous 

 with the horny axis cylinder of tvpical Gorgonias, and hence 

 is endodermal in origin, and that at least the vermiform bodies 

 of the semi-calcareous cylinder are mesodermal in origin. 



If we take a small piece of the end of a branch of this 

 species and carefully expose the axis C3'linder to its very tip, 

 we shall find that the vermiform bodies disappear altogether 

 some distance below the tip. At the very end there is a soft, 

 translucent knob, shaped somewhat like the end of an ordinary 

 tool handle. This seems to be identical in structure with the 

 tip of the axis in ordinary Gorgonias. By commencing at this 



1 "The Anatomy of Invertebi'ated Animals," p. 143. 



2 Comparative Embryology, Vol. I, p. 149. 



