42 GILBERT 0. BOURNE. 



(fig. 14) and it will be easily seen that this peripheral thickeuing 

 of the septa and their fusion to form a theca is due to the 

 activity of the calicoblasts of the inner wall of the extrathecal 

 soft tissues. A reference to Fowler's paper in this number 

 (PL I, fig. 5) shows that in Lophohelia the sutures become 

 indistinct in the lower sections, owing to the addition of this 

 peripheral ring of calcareous tissue from the inner wall of the 

 " Randplatte," as von Heider calls the extrathecal tissues. 

 The same thing is noticeable, but to a much more marked 

 degree, in Oculina, and in it forms the tissue in which the 

 calyces are embedded, i. e. the ccenenchyme. An examination 

 of fig. 6 of this paper shows that in Euphyllia (and it is equally 

 true for Mussa) that the " Randplatten " of adjacent polyps, 

 where the latter have not separated widely from one another, 

 are continuous, and form a covering for the valley separating 

 the two calices. When in a compound coral all the polyps are 

 thus connected the connection is known as the coenosarc, and 

 the ccenenchyme is obviously the product of the calicoblasts of 

 the lower layer of the coenosarc. Fig. 17 is the drawing of a 

 specimen of Mussa distans in the Oxford Museum, a species 

 in which the csespitose type shows a tendency to form a 

 Mseandrine type of colony. Some of the calices are seen to be 

 perfectly separate from one another, and are surrounded by 

 little rings of calcareous matter (ep.) ; whether one calls it 

 peritheca, exotheca, or epitheca does not matter. Where two 

 calices are closely apposed this tissue may be largely developed, 

 and may fill up the valleys completely to the lips of the 

 calices, as in the left-hand corner of the figure (cee.). This is 

 then a ccenenchyme, and a comparison of this figure with fig. 6 

 must irresistibly lead to the conclusion that the two are formed 

 in one and the same manner. In the one case it is looser and 

 has a more adventitious appearance (Mussa), in the other it is 

 more solid and resembles in texture the rest of the corallum 

 (Caryophyllia oculina), that is all. The views here 

 expressed accord very well with Professor Martin Duncan's 

 description of epitheca in some serial coralla (' Linn. Soc. 

 Journ.,' xviii, p. 361), and with what is known of its develop- 



