36 THE GENUS MONTICULIPORA. 



forms which have been placed here are very probably really 

 Polyzoa, and not referable to Montimlipora at all. Others, 

 however, resemble the more normal types of the group in their 

 internal structure ; and I do not at present see how they can 

 be definitely separated from the present genus. Among these 

 I may mention M. Cincinnatiensis, James, M. ttcberculata, E. 

 and H., M. crustulata^ James, and probably M. Ortoni, Nich., 

 all of which I have examined by means of thin sections, and 

 most of which will be subsequently described in detail. 



{/) As a modification of the preceding may be mentioned 

 certain types which consist of moderately but not excessively 

 short corallites, forming a crust which is apparently invariably 

 attached to some particular class of foreign bodies, and which, 

 in consequence, acquires an apparently constant form. As 

 a good example of this group, we may take the curious M. 

 clavacoidea, James. 



II. The Strztcture of the Walls of the Corallites. — Much more 

 important, from a zoological point of view, than the mere form 

 of the corallum, is the minute structure of the wall of the 

 tubes ; and in this respect the Monticuliporoids show wide dif- 

 ferences. The corallites of Moiitinilipora, whatever their form 

 may be, are always contiguous throughout their entire length ; 

 and, theoretically, each tube possesses a perfectly independent 

 and complete wall. In some cases this theoretic and un- 

 doubtedly primitive independence of the calcareous investment 

 of each individual tube is obviously and clearly preserved 

 throughout the entire growth of the corallum. Hence, in 

 thin tangential or longitudinal sections of such forms, the vis- 

 ceral chamber of each corallite is seen to be surrounded by its 

 own investment of light-coloured sclerenchyma, and to be separ- 

 ated from the corresponding investment of all the tubes in 

 immediate contiguity with it by a clearly-marked dark line, 

 which is often thickened into larger or smaller nodes at the 

 angles of junction of the corallites. This permanent preserva- 

 tion of the primitively duplex structure of the wall separating 

 adjoining visceral chambers is seen in many forms, such as 



