INTRODUCTION. 21 



tinned over the pylorus are reflected, upwards again, outside the stomach to cover the lower 

 surface of the disc. Here, moreover, they form the mesenteric folds, upper attach- 



ment is to the under surface of the disc, and whose inner is in part to the ridges of the 

 lips and the corresponding structures on the outside of the stomach. There are openings 

 between these mesenteric folds corresponding with the bases and canals of the tentacules. 

 The pylorus exists more in name than in reality, for the passage into the visceral 

 cavity is large and easily passed. Around the lower margin of the pylorus, and 

 attached where the ridges already alluded to end, are the free edges of the mesenteric 

 folds and a tubular structure?- There is a distinct numerical relation between the 

 development of the ridges, mesenteric foldsj tentacules, septa, and pali. 



If the disc Avere removed from the subjacent corallum by cutting the membrane 

 which is continued from below upwards to its margin, and the pylorus were pulled 

 upwards, the septa, pali, columella, wall, and dissepiments, would be exposed to view, 

 covered by soft tissue ; in other words, all the boundaries of the visceral cavity except the 

 upper would be seen. 



The upper boundary — the under surface of the excised disc — presents a series of 

 radiating soft folds, separated ^^j' intermesenteric spaces, which are perforated by foramina, 

 continuous with the tentacular canals. The pali and septa are developed in these 

 spaces, and hence it is that the tentacules over these hard parts appear to grasp them by 

 their bases. 



The visceral cavity is bounded below and externally by the tissues covering the 

 inside base, the wall,. and the dissepiments which close in the calicular fossa, as the case 

 may be. 



The cavity is divided by the septa and mesenteric folds into a series of radiating 

 fissures, which may be recognised in the dead specimen by means of the interseptal loculi. 

 The absence of the columella and of endothecal dissepiments infers a large visceral 

 cavity, and it may be readily understood that a coral developing endothecal dissepiments 

 rapidly will have a short visceral cavity, for the newest dissepiment bounds the calicular 

 fossa inferiorly. 



The sea-water and its minute organisms would pass into the mouth, through the 

 stomach and pylorus, and would enter between the mesenteric folds into one of the peri- 

 visceral fissures of the great visceral cavity, and the water passes out again through 

 the tentacular canals. 



The under surface of the disc is continuous with the soft tissues covering the septa 

 and wall (internally) by their direct continuation upwards. The contiguity of the tissues 

 covering the costse and outer part of the ioall with the outer rim of the disc has been 

 noticed. 



The disc thus constituted is, when the polype is well nourished and lively, slightly 



1 Plate II, fig. 2. 



