ON THE STEUCTUKE OP PORITES. 487 



On the Structure of Porites, with Prelimiuary Notes on the 

 Soft Parts. By Hb^ry M. Berjtaed, M.A. Cantab., F.L.S. 



[Eead 7th December, 1899.] 

 (Plate 35.) 



In a paper lately read before this Society*, I endeavoured to 

 ascertain the position o£ Porites in the Madreporarian system. 

 A brief sketch of the structure was then given, sufficient to make 

 the rest intelligible. The conclusion arrived at was that Porites 

 resulted from a tendency towards very early budding, already 

 noted in the Madreporidae. This tendency, pushed still further, 

 has produced a genus in which the budding takes place while 

 the skeleton is still immature. In this way, the small size and 

 the shallowness of the calicle, the perforation of the septa, 

 and the reticular nature of the whole skeleton, which may be 

 regarded as retrograde characters, can be reconciled with the 

 presence of a flattened epitheca which, as elsewhere f explained, 

 is characteristic of the highest Madreporarian specialization. 



In the present paper I propose to give an account of the 

 structure of Por^Ye* in greater detail. During the year which 

 has elapsed, my specimens have been examined and re-examined, 

 and new structural details have come to light. One of them, 

 namely, the discovery of the directive plane, and the bilateral 

 symmetry of the calicle, will largely help to rescue the genua 

 from the obscurity to which the smallness of its calicles and the 

 complexity of its reticular skeleton have necessarily condemned it. 



I have also been able to cut sections of the polyps of a 

 West-Indian form, one of the many from that region with low 

 thick knobbed stems, alive only for a few centimetres at the top. 

 A few brief notes on the first results of the microscopical 

 examination of these are here appended. 



The Skeleton. 



Wall and Gcenenchjma. — The distinction often drawn between 



these two J has been due to the absence of any clear conception 



as to what the wall really is. I have already explained in my 



last paper how, in the Madreporidse, the primitive epithecal 



* This vol., p. 127. t Journ. Linn. Soc, Zool. xxvi. p. 495. 



I Compare, for example, Klunzinger's statement that, in Porites, the calicles 

 are united by the walls and not by. a coenenchyma (Corallenthiere, ii. p. 39). 

 The same is repeated by Martin Duncan, Linn. Soc. Journ., Zool. xviii., 1884. 



37* 



