PLATE I. 



MADREPORA MURICATA Linn;, us. 



Fiii. 1. — «, Polyps at the apex of a branch of M. cervicomis. The single apical polyp is larger than the five radial or 

 lateral polyps, and hears only six equal tentacles. 6, An apical polyp viewed from above. The 

 comparative radial extension of the mesenteries can he seen through the transparent discal wall, c, A 

 radial polyp, partly expanded, viewed from the side, d, e, Fully expanded radial polyps viewed from 

 above. ;/, /, Reduced polyps growing on galls produced by the presence of algal growths, h-o, Different 

 polyps of M. palmata; ./', polyp with only ten tentacles; /, a double polyp with two oral apertures; 

 o, two retracted intercalary polyps. Enlarged. 



Fig. '_'. — Longitudinal section through a retracted radial polyp. The polyp is withdrawn within the calice, the 

 actual oral aperture (>». a. ) being situated much below the apex of the corallite. The tentacles (I. I appear 

 as thickenings of the inturned discal wall. On the right side the stomodwal ectoderm is in continuity 

 with the filament at the free edge of a mesentery. The mesenteries and their filaments are convoluted 

 below, and different portions are seen in section. On the left side the gastro-ccelomic cavity is in 

 communication with the superficial canals over the edge of the theca. X 50. 



Fio. 3. — Transverse section through a retracted radial polyp, at about the level t. in the previous figure. The upper 

 part of the polyp is axial and the lower ahaxial in relation to the branch on which it was growing. 

 All the six pairs of mesenteries stretch from the skeletotrophic wall to the inturned disk. A tentacular 

 protuberance arises from each mesenterial chamber, the entocoelic members being larger than the exocoelic. 

 At this level the anterior tentacle (lower in the figure) is no larger than the other entotentacles, while 

 the exocoelic member on each side of it is scarcely seen as a protuberance. The outer column wall 

 (ccenosarc) rests upon twenty-four costal ridges, but no perithecal prolongations of the mesenteries 

 • "•cur. X 50. 



Fig. 4. — Transverse section through the same polyp, at the level of the stomodanim (about in. in fig. 2). The 

 axial-abaxial relations are the reverse of those in fig. 3, that is, the lower side is axial and the upper is 

 ahaxial. X 50. 



Fig. 5. — Transverse section through another polyp, some distance below the stomodwal region. Only three pairs of 

 mesenteries now occur, the other three having disappeared. The black oval bodies in the endoderm of 

 tins and the next figure represent a parasitic Protozoon. X 50. 



Fio. i). — Transverse section through the same polyp at a still lower level. Only two pairs of mesenteries :ire present, 

 but owing to their convoluted character each appears several times in the same section. The polypal 

 cavity is greatly encroached upon by six septal ingrowths. X 50. 

 600 



