488 ME. H. M. BERNAED OK 



wall became flattened out, and a secondary internal septal wall 

 took its place, the living tissues clothing the whole of this septal 

 wall down to the remains of the epitheca. This wall was 

 primitively built up of the radially arranged laminate septa and 

 their synapticular junctions. Secondary modifications occur, 

 and the stiff radial arrangement of plates joined concentrically 

 together dissolve down and change into a sponge-work in which 

 the primitive elements are only just traceable. We then have 

 a reticular wall which may be thick or thin. When a coral with 

 such a septal wall buds, to form a stock, the reticular walls of 

 parent and bud flow together. These comhined walls form the 

 coenenchyma. The coenenchyma can only be said to be absent 

 when it is reduced to a minimum, i. e., when the calicles are 

 separated by a single perforated plate. But, in reality, no 

 sharp line can be drawn between the many degrees of thickness 

 resulting from the fusion of the walls. 



It is true that an apparent distinction exists between the 

 wall and the coenenchyma in certain cases, but in none will it 

 bear examination. In Madrepora, the upper parts of the calicles 

 (when young) project above the coenenchyma, that is, above the 

 fused basal parts of their walls. But as these calicles get older, 

 the fusion usually rises, till, in the basal or older parts of most 

 Madrepores, the calicles are quite submerged, and the fused walls 

 and the coenenchyma are one and the same structure *. 



* It will be noticed that this description tends to limit the meaning of the 

 word ' coenenchyma ' to the fused outer or costal surfaces of purely septate thecse. 

 Its component elements, therefore, are septal and synapticular, — one might have 

 said costal and synapticular. But, in these porous theca, division of radial 

 structures into septal and costal portions can only be artificial. And it seems 

 to me that the word ' costa ' had better be reserved for external ribs which are 

 somewhat more naturally separate from the septa. 



If the term ' coenenchyma' is so limited, it not only excludes such tissues as 

 that in which the calicles of Galaxea are embedded, which is epithecate in 

 origin, but also all the stray proliferations of the skeleton which are frequently 

 met with in the Madreporidse and elsewhere. For instance, in Alveopora 

 there can be no costffi at all, the walls between adjoining calicles being 

 morphologically equivalent to interlacing septal spines (Journ. Linn. Soc, Zool. 

 xxvi. p. 495). And yet, in rare cases, on the undersides of stocks, a curious 

 proliferation of the walls sometimes takes place, so that the calicles may be 

 separated by a coarse reticulum almost like a normal coenenchyma. All such 

 adventitious proliferations of skeleton I propose to call a ' pseudo-coenenchyma.' 

 They are mostly found in the basal parts of stocks, where normally, as is well 

 known, the basal skeleton merely thickens without forming any additional 

 framework. 



