PLATE III. 



MADREPORA MURICATA Linnseus. 



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

 X50. 



PORITES ASTR^EOIDES Lamarck. 



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



Fig. 29. — Transverse section of the same polyp, immediately below the stomodseal region. Rudimentary mesenterial 

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



Fi<;. 30. — Transverse section through a partly expanded polyp. The polyp is somewhat depressed within the calice, 

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

 part of the circular theea, 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 pairs of the primary mesenteries are complete, the dorsal directives having become five, their 

 rudiments being seen still inserted on the stomodseal wall. The stomodseal ectoderm is regularly 

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

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



Fig. 31. — Transverse section through the uppermost region of the calicinal 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-ccelomic cavities of the four polyps are 

 in superficial communication by means of the interseptal spaces. X 50. 

 604 



