MADREPORARIAN CORALS 57 



begin, and also what number of tentacles of the ridges 

 legitimately belong to one polyp and what to the next. It 

 is diihcult to think of an individual which has no well-defined 

 limits. But the difficulties are no less if we try to maintain 

 that a whole valley with its ridges corresponds with the 

 single polyp of a Galaxea. It is quite conceivable that an 

 individual may have two or indeed any number of mouths, 

 or two or a reasonable number of sets of organs. But if we 

 study the anatomy of Meandrina carefully we find that one 

 valley communicates with the others as freely as one set of 

 organs communicates with another in a single valley, and 

 therefore our new proposition leads to the conclusion that 

 the whole set of mouth and organs represents only one 

 individual polyp. Which, it might be said, is absurd. 

 There is no solution to this problem unless there is a perfectly 

 clear conception in the mind of the WTiter or reader of the 

 meaning of the word " individual." The only reasonable 

 solution of the difficulty is, as suggested in Chapter I., to 

 abandon the use of the term Individual as applied to Polyps 

 in organic continuity and to regard the coral as a whole 

 as the only true " Individual." 



EuPHYL LiA. — Another group of Astraeid corals is repre- 

 sented in most large collections by the genera Eusmilia, 

 Euphyllia (Eig. 21), and Mussa. From a thick stem attached 

 to a rock or to another coral the colony divides irregularly 

 into two or three stout branches, which may again subdivide. 

 Each terminal branch ends in a relatively large calyx, in a 

 typical form 20-30 mm. in diameter. The calices may be 

 round or oval or triangular, or more irregular in outline, 

 and they may show the constrictions which are evidence of 

 division by fission. The method of colony formation is 

 technically known as " caespitose," as it has a slight 

 resemblance to the method of branching of some turf 

 plants. 



The septa are numerous and very variable in number, 

 according to the size of the calyx. There seem to be three 

 or more orders of septa. The septa of the first order are 

 large and almost reach the centre of the calyx, those of the 

 second order alternating with those of the first are smaller. 



