48 GILBERT 0. BOURNE. 



The one form which must be placed in a separate group is 

 Flabellum. It possesses no " Randplatte," its calyx therefore 

 cannot grow peripherally, and in section it presents an entirely 

 different appearance to any other coral. Fowler gives accurate 

 drawings of sections of Flabellum in his latest paper 

 (" Anatomy of the Madreporaria," iii), and it is not worth 

 while to reproduce them. His explanation, however, is not 

 quite adequate to explain the phenomena. If we assume that 

 Flabellum develops on the type of Astroides — and from the 

 anatomy of the adult we have no right to assume that it 

 develops otherwise, it is impossible to see how the theca could 

 have been formed by fusion of the peripheral ends of the septa, 

 and yet no soft parts left external to the theca. To understand 

 this the reader must mentally follow the processes of growth 

 with the aid of figs. 13, 14, and 15, up to the adult condition. 

 My view of the so-called theca of Flabellum is that it is really 

 a basal structure which has grown upwards to form a calyx, in 

 a manner analogous to the opposite process by which the theca 

 of Fungia has flattened out to form an apparent basal struc- 

 ture. The base would always lie actually, as well as appar- 

 ently, external to the polyp, and would entirely enclose it. It 

 could only be added to on its inner side, and thus Fowler's 

 interpretation of the appearance of the centres of calcification 

 would continue to hold good. Moreover, the peculiar appear- 

 ance of infolding towards the centres of the septa, figured but 

 not discussed by him, would receive a sufficient explanation 

 when we consider that the septa are formed continuously with 

 the basal plate, and within folds of the three layers, each of 

 which necessarily includes two layers of calicoblasts. The 

 form of the corallum exhibits in fact the relation of the 

 primary folds of tissue within which the septa are developed. 

 The sutures — which, it must be observed, do not reach to 

 the exterior of the " theca " — would necessarily result 

 from the further growth of the septa. If I am right in consi- 

 dering epitheca to be continuous with and indistinguishable 

 from the basal plate, my views on Flabellum coincide 

 curiously with those of von Koch, who regards the apparent 



