192 Notes on Some Actinians from the Bahama Islands, 



are quite conspicuous." I can add to this statement as to the 

 distribution of the tubercles the fact that the tubercles are more 

 numerous and more perfectly developed upon one side of the 

 column than on the other, the arrangement described by Haddon 

 and Miss Shackleton ('91) for I. asymmetricus being thus recalled. 



The column wall is very much thinner than that of /. tubercu- 

 latus and in addition does not show any of the large canals filled 

 with cells, so abundant in the Bermudan form. Numerous 

 canaliculi and scattered cells, the latter frequently placed in the 

 canaliculi, occur, the mesogloea being otherwise structureless. 

 The ectoderm of the column presents the arrangement which is 

 usual in Zoanthids, being covered by a layer of mesogloea, the 

 subcuticula, from which trabeculae extend inwards to unite 

 with the general mesogloea, cavities being thus formed which en- 

 close packets of ectoderm cells (Qg. 1). Externally to the sub- 

 cuticula is a delicate euticula to which foreign particles adhere, 

 and the ectoderm cells contain numerous Zooxanthellse. This 

 arrangement is identical with what I have described for J. tuber- 

 culatiis ('89a), and agrees in its essential particulars with the ac- 

 counts of the majorit}^ of the authors who have given the matter 

 their attention. Quite recently von Heider ('95), in his account 

 of Zoanthus chierchise, has come to the conclusion that the 

 trabeculse which separate the various packets of ectoderm are cells 

 and that the subcuticula is formed b}^ the fusion of their outer ends. 

 Such an interpretation of the appearances is certainly not ap- 

 plicable to either of the species of Isaurus I have examined ; the 

 trabeculae are so thick that their continuity with the mesogloea is 

 beyond question, aiid, furthermore, the structure of the sub- 

 cuticula shows it to be identical with the matrix of the mesogloea. 

 Nor do the appearances presented by such a form as Zoanthus 

 sociatus warrant the belief that the trabeculse are otherwise con- 

 stituted than in Isaurus, and so far as my observations are con- 

 cerned they tend to show that the conclusions of von Heider are 

 erroneous. 



The tubercles are thickenings of the mesogloea, but each con- 

 tains also a cavity lined with cells continuous with the endoderm. 

 Dr. Northrop's notes contain the following description of the 

 tubercles : '' In places the mesogloea contains on its inner side 

 deep cavities which are lined by thfr endodermi&. The muaaular 

 layer of the mesogloea, however, does not enter the cavity, but 



