CALCAREOUS SKELETON OF THE ANTHOZOA. 499 



Studies on the Structure and Formation of the 

 Calcareous Skeleton of the Anthozoa. 



Oilbcrt C. Bourne, ]^I.A., F.L,.S., 



Fellow and Tutor of New College, Oxford ; University Lecturer in Compara- 

 tive Anatomy. 



With Plates 40—43. 



Milne Edwards and Haime, and the older authors on coral 

 structure, regarded the calcareous skeleton of the Madreporaria 

 as a calcified mesoderm. In 1881 Dr. A. von Heider, of 

 Graz (11), described a layer of rounded cells underlying the 

 corallum of Cladocora, and named them calicoblasts, since he 

 judged from their position that they must be the coral-forming 

 elements. In the following year G. von Koch (17), in a 

 memoir on the development of Astroides calycularis, con- 

 firmed the observation of von Heider, and further demonstrated 

 the fact that the calicoblast layer is a product of the basal 

 ectoderm. 



Von Koch described the first elements of the corallum as 

 making their appearance between the basal ectoderm and the 

 surface to which the larva attaches itself, and he described the 

 first formed calcareous particles as " crystalline spheroids/' 

 which increase in number and eventually fuse together. " Bei 

 Astroides bildet sich aus dem Ektoderm der Fussscheibe zuerst 

 eine diinne Kalkplatte, welche sich irgend einer Unterlage 

 anlegt, und die Fussplatte des spatern Polypars darstellt. Sie 

 eusteht aus krystallinischen sphseroiden Korperchen, welche 



