INTRODUCTION. 21 
tinued 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 ¢vbular structure There is a distinct numerical relation between the 
development of the ridges, mesenteric folds, tentacules, septa, and pall. 
If the disc were 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 dy 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 
Jissures, 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. he contiguity of the tissues 
covering the coste and outer part of the wal/ 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. 
