THE ANATOMY OF THE MADREPORARIA. 429 



Fig. 3. Amphihelia ramea. — The body wall seen by transmitted light. 

 The darker parts represent the canals, the lighter the ridges of coral between 

 them. 



Fig. 4. Stephanophyllia formosissima. — Ideal diagrammatic representa- 

 tion of the relations of septa, mesenteries, costar, and body wall to each other, 

 in a small cube cut out from the base of the polyp. Ectoderm, "blocked" black 

 and white ; mesogloea, thick black line ; endoderm, thin black line ; corallum, 

 dotted. Two radial trabecular (to which transparent mesenteries are attached) 

 are cut across in the front part of the diagram, showing their connection with 

 the body wall. From two other radial trabecular rise two septa, not touching the 

 body wall at any point ; of these septa the left-handmost is cut between two 

 concentric trabecular, and the other at the point where concentric trabecula, 

 radial trabecula, and septum meet. A synapticulum braces together the two 

 septa, perforating the right-hand mesentery (v. p. 6). 



Fig. 5. Stephanophyllia formosissima. — View of a complete mesen- 

 tery, with the basal (thecal) tissues attached. In the latter is seen the row of 

 holes left by decalcification of the concentric trabecular ; and in the mesentery 

 four perforations produced by synapticular, at the sides of which the muscle 

 pleatings are gathered into characteristic bundles (v. p. 7). 



Fig. 6. Stephanophyllia formosissima. — Two transverse sections taken 

 at the base of a mesentery. In A, the higher of the two, the concentric 

 trabecular have cut the mesentery across, so that a series of plates resembling 

 the one here drawn {31) is produced along the whole radius (cf. the condition 

 in Fungia, Bourne, 'Quart. Journ. Micr. Sci.,' xxvii, PI. XXV, fig. 13). In 

 the plane of B, the section passes through a radial trabecula also, and is thus 

 taken below the edge of the mesentery. In both sections are seen the pro- 

 cesses for the firmer attachment of the mesentery (v. p. 8). The arrows 

 indicate the direction of R., the radial, and C, the concentric trabecular. 



Fig. 7. Flabellum alabastrum. — Lateral view of the distal edge of the 

 mesogloea lamina of a mesentery, i.e. of the edge which is attached directly to 

 the corallum (cf. "Anat. Madrep.," i, fig. 2), showing the laminated pro- 

 cesses of attachment of the mesentery (v. p. 8). 



Fig. 8. Flabellum alabastrum. — Transverse section of the base of a 

 mesentery (3/.), showing the processes of attachment lying in the space from 

 which corallum has been removed. Those which are radially laminated are 

 probably seen in transverse section, while parallel lamination isdicates oblique 

 section (cf. Sclater, 'P. Z. S.,' 1S86, pi. xiv, figs. 11—13). 



Fig. 9. Sphenotrochus rubescens. — Transverse section through the 

 sphincter muscle (" Rotteken's muscle"), which draws the mouth-disc over the 

 tentacles. 



Fig. ]0. Sphenotrochus rubescens. — Transverse section (incomplete) 

 through a pair of mesenteries and the surrounding tissues. Ectoderm and 



