/ 



PLATE III. 



MADREPORA MURICATA Liniueus. 



Figs. 22-27. — Series fif sections through the coenosaro, illustrating the formation of a bud. For explanation, see p. 497. 

 X50. 



PORITES ASTR^OIDES Lamarck. 



Fig. 28. —Transverse section through the upper stomoda^al region of a partly expanded polyp. X 110. 



Fig. 29. — Transverse section of the same i)olyp, immediatel)- bel<ivv the stomod;cal region. Rudimentary mesenterial 

 filaments occur on only the first three developmental pairs of mesenteries. X 110. 



Fig. 30. — Transverse sectiim through a jiartly expanded polyp. The polyp is somewhat deiwessed within the calice, 

 so that the middle of tlie section includes the stomodical region, and the periphery includes the greater 

 part of the circular theca, the two wholly separated from one another except at a narrow region on the 

 right side. Within seven of the twelve primary mesenterial chambers is a transverse section of an 

 introverted tentacle ((.) , the apex of the tentacle being represented in four of the sections by a specially 

 thickened region. The ectoderm of the tentacles is now internal, and the endoderm external. Only 

 three i)airs of the i)rimary mesenteries are complete, the dorsal directives having become free, their 

 rudiments being seen still inserted on the .^tomodfcal wall. The stomodical ectoderm is regularly 

 folded, but in a different manner from fig. 28. The double cohnnn wall ceases a few sections below, and 

 the continuity of the mesenteries, from the thecal wall to the stomodicum, is then established. X 50. 



Fig. 31. — Transverse section through the uppermost region of the caliciiial edge common to four contiguous polyps. 

 The partial limits of the four polyps are shown by four curved lines. Rudiments of eight exsert septa 

 occur, and the first indications of two mesenteries. The gastro-coelomic cavities of the four polyps are 

 in superficial (■onnnunication by means of the interseptal spaces. X 50. 

 604 



