﻿ANACROPORA. 169 



The caliclcs. — True protuberant calicles are not characteristic of the Montiporfe proper.* 

 They may and frequently do appear in the younger portions of the stock which consist solely 

 of the often thin primitive streaming layer. Out of this they frequently emerge and are 

 then naturally tilted towards the direction of growth. As, however, the corallum thickens, 

 the thickening layer submerges the protuberance so that the calicle comes to open level 

 with the surface of the coenenchyma. In Anacropora, the thickening cortical layer usually 

 remains thin, and those calicles which grow faster than the cortex round the streaming axial 

 strand rise as true protuberant calicles. This protuberance of the calicles, which may 

 sometimes be suppressed (A. spinosa), gives the otherwise uniformly cylindrical stems and 

 older branches the knotted appearance of a blackthorn stick. 



As these calicles rise above the surface, the radial elements of their walls may become 

 more and more pronounced. And these, when best developed, are frequently seen to be 

 laminate, the same plate occasionally projecting into the polyp cavity as a septum and down 

 the outer wall as a costa. This, it should be especially noted, is best seen in the most 

 protuberant calicles. In those less protuberant, and hence most like the submerged calicles of 

 Montipora, the radial laminae are not visible, and the septa appear, as is typical of MontijMva, 

 as vertical series of projecting spines. 



These points are of great morphological interest and serve to establish the true relation- 

 ship of Anacropora and Montipora. 



III. DEFINITION OF THE GENUS. 



Anacroporfe may therefore be defined as branched Montiporinse which, owing to the 

 typical divergence of the thin branches at wide angles, tend to form low matted tangles rather 

 than arborescent stocks, and in which many of the calicle walls grow faster than the feebly 

 developed cortical layer, and are thus protuberant ; the laminate radial elements typical of 

 Madreporidffi, but lost in Montipora, reappear in the protuberant walls as septa and costse. 



IV. RELATION OF THE GENUS TO MONTIPORA.f 



Assuming then the close relationship of these two genera, we are, I think, justified in 

 regarding Montipora as the more primitive. Its simple explanate method of growth must have 

 preceded the highly specialised branching of Anacropora. On the other hand, the protuberant 

 caHcles with laminate radial structures suggest that the genus branched off from the common 

 ancestor before the calicles were quite as degenerated, or rather stunted, as they now are in 

 Montipora. The markedly laminate character of the axial layer, which is now so frequently 



* On the two kinds of false protuberance seen in this genus, see pp. 10-1 L 

 t The inter-relationships of the Madreporidse set forth in this volmne were accepted by Brook 

 (J. Lmn. Soc, xxiv. 1893), though from a diflferent morphological standpoint. 



