570 SYDNEY J. HIOKSON. 



•' (a) In the first place there is the very important and remark- 

 able difference in the minute structure of the calcareous 

 skeleton in the two types in question. In Tubipora the 

 corallum is made up of fused calcareous spicules, which are 

 so disposed as to give rise to a universally distributed system of 

 minute canaliculi or tubuli, which open on both the outer and 

 inner surfaces of the skeleton by well-marked apertures. The 

 size of these tubuli is comparatively so great that it is quite 

 impossible that their presence could be overlooked in thin sec- 

 tions of Syringopora, if they really existed in this genus. On 

 the other hand, the skeleton of Syringopora, as regards its 

 minute structure, is quite compact, and shows no signs what- 

 ever, either of being penetrated by a system of tubuli, or of 

 being formed by the fusion of ectodermal spicules." It is 

 difficult to see why this difference should be considered of any 

 great morphological importance. The size of the pores or 

 " tubuli," as Professor Nicholson calls them, varies consider- 

 ably in the different regions of the corallite, being at the younger 

 ends much larger than they are at the older ends, so that it is 

 evident that as the corallite grows older the tubuli have a ten- 

 dency to be filled up, and a still further continuation of this 

 process would make the wall of the corallite quite aporous. I 

 have no evidence to prove that the complete filling up of these 

 perforations in the walls ever does occur in Tubipora, but 

 should an example be found in which this has occurred I should 

 certainly not consider it sufficient reason for the formation of a 

 new genus or even a new species. That the skeleton of Syrin- 

 gopora " shows no signs of being formed by the fusion of ecto- 

 dermal spicules" is not to be wondered at, as we possess no 

 means of studying either the development or the growth of the 

 skeleton of this form, since the delicate growing ends would be 

 broken down and destroyed ; and even in recent genera (such 

 as Corallium, Lacaze-Duthiers), in which the skeleton is known 

 by an examination of its growth to be composed of fused 

 spicules, no evidence of them can be seen in thin transverse 

 section through the hard parts. 



The second difference urged by Professor Nicholson as being 



