ANATOMY OF MUSS A AND EUPHYLLIA. 43 



merit. Beginning at the stage of development drawn in fig. 13 

 and mentally following the epitheca through its succeeding 

 stages, we see that it is really a basal structure to begin 

 with, and that as growth proceeds it follows the edge of 

 the " Randplatte " as the latter retreats farther and farther 

 from the base. Where a compound colony is formed by 

 lateral budding, and the ccenosarc represents the united 

 " Randplatten " of all the polyps, the epitheca will form a 

 lamellar structure at the bases of the polyps. Where, as in 

 the serial coralla Porites and Leptoria, the septa of adjacent 

 polyps fuse together, and there is no theca proper separating 

 the interseptal loculi of the two, it can easily be understood 

 how the epithecal nodules described by Professor Duncan 

 would be formed in early stages of growth. 



It is obvious from the foregoing that the differences between 

 the tissue which is early laid down to consolidate the theca, 

 and coenenchyme, and epitheca, depend on quantity and texture, 

 and not on the region of the polyps from which they are 

 formed. 



In my description of Mussa and Euphyllia I have referred 

 to the existence of dissepiments. An examination of figs. 3 

 and 4 shows that these oblique partitions running across the 

 interseptal loculi are formed from the calicoblasts of what 

 were originally the interseptal parts of the base of the polyp. 

 The soft tissues do not occupy the whole of the cavity of the 

 calyx except in its uppermost part, but slope off to a point 

 below. An examination of fig. 4 shows the relations of these 

 parts to the dissepiments, and fig. 3 shows that the spaces 

 between the dissepiments and the theca are not occupied by 

 any soft tissues whatever. There are probably periods of 

 active coral secretion alternating with periods of reproduction 

 in these polyps. During the latter period the thin dissepi- 

 ments are formed by the basal tissues, whilst in the former 

 period the septa increase greatly in height, the polyp is, as it 

 were, moved higher up upon its stem, and deserts the old 

 dissepiments upon which it was resting. Then follows a new 

 period of reproduction, during which new dissepiments are 



