i6o TABULATE CORALS. 



lltes are essentially in contact with one another — if not invari- 

 ably, certainly as a general rule — throughout their entire length; 

 though occasionally limited tubular spaces are left at the point 

 of junction of three or four of the corallites.^ Moreover, thin 

 transverse sections (PI. VII., fig. 2 a) prove incontrovertibly 

 that the walls of the corallites are firmly amalgamated with one 

 another, the junction between contiguous tubes being marked 

 by a wavy dark line. Occasionally, as just remarked, the sec- 

 tions show a tubular space at the angles of junction of the 

 corallites, and these spaces are definitely circular or oval, and 

 are accompanied by smaller rounded and definite vacuities (PI. 

 VII., fig. 2 b), which are situated in the substance of the walls 

 themselves. These spaces I regard as being cross-sections of 

 tubes which pass through the thick walls longitudinally, and as 

 being, therefore, of the same nature as the canals which I have 

 described in PleiLrodidyum under the name of " intramural 

 canals." Similar tubes occur in the walls of Lyopora, Nich. 

 and Eth. jun. ; and though I am uncertain as to their true 

 nature, they are clearly endothecal, and cannot be of the nature 

 of " coenenchymal tubes." They are, further, very minute, and 

 only the largest of them would be recognised by the use of a 

 hand-lens upon actual specimens. Vertical sections (PI. VII., 

 fig. 2 c) entirely confirm the evidence derivable from transverse 

 slices as to the absence of anything which could properly be 

 called coenenchymal. The walls, as before, are firmly united, 

 and the boundary between contiguous tubes is marked by a 

 sinuous dark line, occasionally interrupted by an irregular or 

 oval space. The septa are best studied in transverse sections 

 (PL VII., figs. 2 a and 2 b), though excellently seen in the actual 



^ Occasional and partial absence of complete contact between the tubes is by no 

 means an unusual phenomenon in genera in which the corallites are normally and 

 regularly polygonal and accurately contiguous. Thus, in Coluinnaria {Favistelld) 

 alveolata, Goldf., it is not uncommon for the tubes close to their mouths to become, 

 in parts of the corallum, slightly separate, in which case they are also subcircular, 

 though the corallites are ordinarily prismatic and in close contact. In Coluinnaria 

 {Favistella) calicina, Nich., again, some of the corallites are always more or less 

 disjunct and subcircular, while others are always polygonal and firmly united by 

 their walls. 



