MADREPORARIAN CORALS 83 



that each calyx is shut off b}' a thin tabula from a little 

 chamber below it, and this again by another thin tabula 

 from another chamber of the same diameter, or, to put 

 the same thing in another way, the corallum is perforated 

 by a number of radial tubes which are divided by thin 

 plates of coral substance into a series of closed chambers, of 

 which the outermost one is freely open to the surface and 

 forms the calvx. The Seriatoporidae are in fact Tabulate 

 corals. 



Further, the same sections or fractures will show 

 that apart from these chambers the corallum is quite 

 solid and there are no communications between one set 

 of chambers and another. They are in fact imperforate 

 corals. 



Our knowledge of the characters of the polyps is based on 

 the study of only a few specimens, but there seems to be 

 no doubt that as a rule the polyps are provided with twelve 

 short tentacles and twelve mesenteries, of which two pairs 

 are directive mesenteries. The tentacles of a species of 

 Seriatopora described by Fowler are capitate in form and 

 show the very remarkable and, in Madreporaria, unique 

 character of being introverted during retraction. 



The polyps are connected with one another by a thin and 

 entirely superficial layer of coenosarc supported by the spines 

 of the coenosteum, and in this runs a delicate network of 

 nutritive canals. This elaborate system of canals, running 

 entirely superficially to the coenosteum, is similar to the 

 system of canals which connect the polyps in some of the 

 perforate corals, such as Madrepora and Dendrophyllia, but 

 in the case of the latter is continued downwards into the 

 perforations which traverse the coenosteum. 



In the description of corals, pathological conditions are 

 not usually mentioned, and considerations of time and space 

 often render such a course imperative. But in this family 

 there is one kind of pathological change which is of excep- 

 tional interest. Like other corals, Pocillopora and Seriato- 

 pora may be attacked by certain barnacles, worms, and 

 mxolluscs in such a way as to modify in some way the normal 

 method of growth, but they are also liable to what may be 



