PLATE II. 



MADREPORA MURICATA Linnwus. 



Fio. 7. — Transverse section through a portion of the external covering of the skeleton (ccenosarc) and the superficial 

 longitudinal canals. The outer endodenn of the canals is crowded with zooxanthella-, while they are 

 more sparse internally, where the endoderm is narrow. The calicoblast layer has almost disappeared, 

 but the denser part of the skeletal matrix remains, associated with desmoidal processes. X 320. 

 Fi<;. 8. — Transverse section through the tissues covering the uppermost part of the skeleton of an apical polyp, 

 representing a superficial canal and part of one adjacent on the right side. The outer ectoderm is 

 much broader than in the previous figure, and the calicoblast layer [cal, ) is also better developed. The 

 endoderm lining the canals is devoid of zooxanthelhe, and the mesogloea is only a mere lamella. 

 X 320. 

 -Cells from the ccenosarc: <i, Two varieties of nematoblasts; '>, supporting cells; c, granular cell from 



endoderm, containing two zooxanthella 1 . X 450. 

 -Transverse section through a portion of a tentacle showing the well-developed nerve layer (nr. I. I, the 



cnidocils, and cilia on the ectoderm and endoderm. X 320. 

 -Longitudinal section through the disk and uppermost part of the stomodseal wall. X 320. 

 -Transverse section through two mesenteries (directives), and the stomodseal wall and skeletotrophic 



tissues to which they are attached. X 300. 

 -«, Two gland cells from the stomod;eum; b, group of ciliated supporting cells from the stpmodseum. X 450. 

 -Transverse section through a mesentery, terminated by a mesenterial filament. X 320. 

 -Cells from mesenterial filament: «, various gland cells; /', nematoblast; c, supporting cells from posterior 

 region of filament; <I, cell with zooxanthelhe from the mesenterial epithelium. X 450. 

 Fig. 16. — Transverse section through a canal near the apex of a branch, showing the deep calicoblast layer, and the 



narrow ciliated endodermal lining of the canal. .■ 320. 

 Fig. 17. — Section through a decalcified canal wall some distance from the apex. X 320. 



Fig. 18. — Section through the wall of a canal, and a portion of the organic matrix remaining after slow decalcification. 

 The section is taken from neartbe growing apex of a branch. Toward the upper part the matrix is still 

 connected with the canal wall, but elsewhere has become shrunken from it. The matrix shows no 

 cellular structure, but in appearance very closely resembles the actual skeleton as seen in surface view 

 (c/. fig. 19). x 320. 

 Fig. 19. — Surface view of part of the macerated corallum near the growing apex. X 320. 



Fio. 20. — Mesentery from a bud, showing the early development of the mesenterial filament; the latter is at first 

 indistinguishable from the mesenterial epithelium. X 320. 

 602 



