INTRODUCTION. 3 
On looking into a calice and down the internal cavity the vacant spots between the 
septa become apparent; these are the interseptal loculi; they are restricted in depth 
when dissepiments exist, and extend from the bottom to the calice when there is no 
endotheca.* 
The septa vary in size, and may or may not reach from the wall to the columella, and 
all the space left between them, restricted or not by dissepiments or tadule’* (horizontal 
dissepiments), forms in living corals part of the visceral cavity. When there is no 
columella there is a central space, into which the interseptal loculi open; the visceral 
cavity is then all the larger, but the depth of its inferior boundary always depends 
upon the existence of the endotheca. The septa are frequently raised in an 
arched form*® above the level of the top of the wad/ (theca); and a line carried 
across their tops over the calice would bound a cavity whose base is the top of the 
‘columella and the internal ends of the septa. ‘This cavity is the calicular fossa ; 
the interseptal loculi open into it, and it is very variable in size and depth. When 
the columella is very prominent the calicular fossa is all the more restricted in depth ; 
but when the wall is high, the columella absent, and the septa not exsert, the fossa is 
deeper. 
It. will now be evident that the hard parts of a coral form the boundaries to a 
system of cavities (the interseptal loculi), and to the calicular fossa, into which they 
open. 
The disc, in living corals, elevated very slightly above the tips of the septa, closes 
the calicular fossa above, and opens into it over the coiumella, so that when the mouth 
is widely open the markings on the free surface of this structure can be seen faintly 
covered by the tissue which lines all the hard parts of the coral above the newest 
dissepiment or the base, as the case may be. 
The septa, dissepiments, and the columella, being covered with a soft tissue, which 
is continuous with the margin of the disc, it is evident that there is a cavity in the soft 
parts of the coral which corresponds with that already mentioned as being within the 
calcareous portion. 
Thus, the interseptal loculi, calicular fossa, and the space between the tops 
of the septa and the disc, all lined by continuous soft tissue, form the whole viscera/ 
cavity. 
The mouth, seen on the upper surface of the disc, opens into a short stomach, which 
in its turn opens into the visceral cavity by means of a pyloric orifice situated above the 
level of the top of the columella (or junction of the inner ends of the septa when there is 
no columella). 
The stomach is an inversion of the membranes of the disc, is tubular, ridged longi- 
1 Plate I, figs. 5, 14. 2 Plate III, figs. 9, 11, 16. 3 Plate I, figs. 4, 14, 15. 
