504 GILBERT C. BOURNE. 



are doubtless traces of organic matter. The figures certainly 

 do not show to demonstration that the scales are what Mrs. 

 Gordon claims them to be, calcified cells. And though she 

 identifies the scales with the striated structures called calico- 

 blasts by von Heider, she does not bring forward any new 

 evidence, either in drawings or in the text, to show that the 

 striated structure of the scales of Galaxea, and of von Heider's 

 calicoblasts, is due to one and the same cause, viz. the presence 

 of spicules of carbonate of lime. 



It is easy to make a preparation from the vesicular exotheca 

 of Galaxea, showing the scale-like calcareous structures figured 

 by Mrs. Gordon (loc. cit., figs. 8a, 8b), and it may be conceded 

 that their resemblance to the striated structures identified by 

 von Heider as calicoblasts is sufficiently striking. But we 

 liave no evidence that the striated structures are found in this 

 position in the fresh polyp ; we have no evidence that the 

 striations of von Heider's calicoblasts are due to the formation 

 of spicules within them ; but, as 1 shall show directly, we have 

 evidence to the contrary, and from the analogy of other corals 

 there is evexj reason to believe that the striated structures are 

 not present in the soft tissues covering the exotheca. 



Nor can I entirely agree with Mrs. Gordon's description of 

 the superficial emergences of the corallum in Galaxea and 

 other corals as " scales." 



It will appear in this paper that the surfaces of certain corals 

 present an appearance like that described for Galaxea, but 

 that the apparent scales are really due to the emergence of 

 bundles of parallel crystalline fibres at the surface of the 

 corallum. But before going further into this question I will 

 give the results of my observations on the structure and 

 formation of the spicules of Alcyonaria. Since we know that 

 these spicules are entoplastic products, it seemed to me that a 

 knowledge of the minute structure of the spicule might assist 

 in the interpretation of the minute structure of the Madre- 

 porariau corallum. Throughout this paper the word " spicule " 

 denotes an entoplastic product of a single cell or of a coeno- 

 cyte. 



