68 



THE ANTHOZOA 



above, induce modifications in the process. The canal system 

 which permeates the porous theca becomes much extended, and, as 

 it extends, calcareous tissue is deposited between the network of 

 canals, so that the theca appears to be enormously thickened. 

 But the mesenteries do not share in this extension, and so the 

 edge-zone proper — that is to say, the soft tissue which is external to 

 the calyx, and is supported on prolongations of the mesenteries — 



Fio. XXXII. 



1.— Section through a braiichlet of Madrepora, sp. ? showing an axial zooid with septa, the 

 surrounding coenenchyme, and two buds, h, b'. 



2.— Diagram of a longitudinal section of Mailrrpora dvririllei, showing the perforations 

 in the stonio<laeuin leading into canals hollowed out in the mesenteries. M, mesentery ; .s', 

 septum ; Th, theca ; 7's, perisarc. 



3. — Diagram of tlie various fonns and conditions of the mesenteries in a zooid of Maiirrpma 

 durinlki. 'Dw nii'scnteries numbered 1,1; 2, 2 ; 8, 3, and bear no tllament and are simple ; tho 

 remainder are moditied, and bear filaments below the level of the stonio<iaeum. 



4. — niagram of a transverse section of a zooid of the same species. Ps, perisarc. 



f). — Tnmsverso section of a modilled mesentery of A/, dnrvillei, passing through two ami. •» 

 of the stomodajal canal. Tlie thickened endoderm of the moditied mesentery is clearly seen. 



(1 original ; the rest after Fowler.) 



becomes limited to the neighbourhood of the mouth of the calyx. 

 The rest of the coral is clothed with a coenosarc in which no traces 

 of the mesenteries are discoverable. From this coenosarc buds 

 arise which grow into zooids whose cavities are permanently con- 

 nected with the cavities of the other zooids composing the colony 

 by means of the system of canals just spoken of, as well as by 

 the canals of the coeno.sarc (see Fig. XXX. 1, and Fig. XXXII. 

 1, 4). It is clear that in the perforate corals the spongy tissue 



