OF COEXOPSAMMIA FROM LIFV. 361 



coelentera at frequent intervals communicate with the coenosarcal canals by ramifying 

 canals through the theca. 



The coenosarcal canals in fact are simply extrathecal portions of the coelentera of 

 the diflferent poh-ps, which serve to connect theii- intrathecal or gastrovascular portions. 



Peritheca and coenosarc. The corallum except over the base of attachment 

 is everywhere covered by the calicoblast layer of ectoderm. This is constantly depositing 

 skeleton over all parts more or less rapidly. Skeleton so deposited has been termed 

 by Martin Duncan (5), when it occurs outside the theca and between the costae, the 

 " exotheca," and, when it serves to fill up the valleys between the free portions of the 

 corallites, the " coenenchyma." Indeed, when the deposit of corallum outside the corallites 

 was small, Martin Duncan called it "exotheca," but, if considerable, " coenench}"ma." 



In the asexual method of reproduction, which forms the colony, whether by fission 

 or bud formation, there is at first no coenenchyma between the two individuals, or 

 between the bud and its parent corallite. In individual specimens of any species the 

 coenenchyma varies enormously with the rate and form of growth of the colonj' ; it 

 hence seems to me improbable that its relative abundance alone can be in any genus 

 a specific distinction. There is no sharp line of sepai-ation nor of structure between 

 the "exotheca" and the "coenenchyma" in Coenopsammia, nor indeed in most Madre- 

 poraria, the latter as it is built up being necessarily fused with the former. In 

 Galaxea however the distinction is well marked, the "coenenchyma" having a porous 

 and the "exotheca" a compact structure. 



It hence appears to me advisable that the term "coenenchyma," if retained in 

 the Madreporaria, should be applied either to the structure usually so-called in Galaxea 

 or to all parts of the corallum outside the theca. The term is of such wide application 

 that it would onlj" increase the confusion, which already prevails, to restrict it in such 

 a way. Either use of the term too is du-ectly opposed to its w-ell-established use 

 in the rest of the Anthozoa. I accordingly propose to use the term peritheca, which 

 was employed in the first place by Milne Edwards and Haime for the so-called 

 "coenenchyma" of Gala-xea. The peritheca is that part of the corallum of colonial 

 Madreporaria, which is deposited outside and subsequentlt/ to the theca. The coenosarc is 

 that part of the polyps in a colony which lies outside but not above (i.e. in expanded 

 state) the thecae of the several corallites. The " Randplatte " of Heider and von Koch, 

 the "edge-zone" of Miss Ogilvie, is then that part of the coenosarc which lies over 

 the free portions of the corallites. The above use of the term coenosarc is more in 

 accordance with its physiological meaning in the Alcyouaria and Hydrozoa. 



The expanded polyp. As all the polyps of the specimens, entrusted to me by 

 Dr Willey, are completely retracted, it is impossible to speak definitely of the conditions 

 found in the living polyps. However, from the appearance of the contracted muscles 

 and the accordingly much bent mesenteries, I am led to believe that the polyps 

 expand themselves to a height of at least 4 mm. above the top of the theca. The 

 tentacles then form three circles close to one another round the peristome, or mouth- 

 disc, the outer with twelve, and the two inner each with six tentacles, the bases of 

 the outer and the two inner circles alternating with one another. 



