INTRODUCTION. 3 



On looking into a calice and down the internal cavity the vacant spots between the 

 septa become apparent; these are the interseptal locidi ; they are restricted in depth 

 when dissepiments exist, and extend from the bottom to the cahce 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 tabulcs^ (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 loall (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 wJien the Avail 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 columella, 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 M'ith that already mentioned as being within the 

 calcareous portion. 



Thus, the inierseptal loculi, calicular fossa, and the space between the tops 

 of the septa and the disc, all lined by continuous soft tissue, form the whole visceral 

 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. ^ pjate III, figs. 9, 11, IC. ^ Plate I, figs. 4, 14, 15. 



