242 CEYLON PEARL OYSTEE REPORT. 



Fig. 16. Section through the ectoderm of the body-wall of Heterocyatkus. gl., gland cells, mg., mesoglcea. 



n., n., nematocysts. nv., nervous layer. Zeiss. Imm. T V. Comp. Oc. 4. 

 17. Section through the inner end of one of the canals leading into the Aspidosiphon chamber in 



Heterocyatkus. gl., gland cells. n., ., ovoid nematocysts with granular contents. Zeiss. 



Imm. jlj. Comp. Oc. 4. 

 18. A nematocyst O06 millim. in length from the convoluted mesenterial filaments of Heterocyatkus. 

 ,, 19. Endoderm covering the septa of Heterocyatkus showing gl., glandular looking cells, which may be 



degenerate nematocysts. An isolated cell is shown to the right of the figure, zo., zooxan- 



thellae. Zeiss. Imm. yV. Comp. Oc. 4. 

 20. Endoderm of Heterocyatkus showing am., amoeboid cells full of granules, cal., calicoblasts. 



Zeiss. Imm. T V. Comp. Oc. 4. 

 21. Columnar endoderm from the axial gastro-vascular cavity of Heterocyatkus. 

 22. Semi-diagrammatic representation of a horizontal section through Heteropsammia micJwlini a 



little above the stomocheum. The corallum is black. The mesenteries, peristomial, tentacular 



and external ectoderm are represented by red lines. 1, 2, 3, the several cycles of endosepta. 



4, a single endoseptum of the 4th cycle. D., the single pair of directive mesenteries. t.\ t?, 



t. 3 , the several orders of tentacles, introverted and doubled over the endosepta. 

 ,, 23. Ectoderm of the body-wall of Heteropsammia michelini. en., endoderm. gl.l, goblet-shaped 



gland cells with granular contents, gl.l, flask-shaped gland cell, mg., mesoglcea. n.\ spiral 



nematocysts. n. 2 , large nematocyst. zo., zooxanthellre. Zeiss. Imm. T V. Comp. Oc. 4. 

 ,, 24. Transverse section through a canal leading into the A sjridusiphon chamber in Heteropsammia. 



The histological details are indicated diagrammatically. ec, ectoderm lining the canal. 



en.c, endoderm canals surrounding the central ectodermic canal, mg., mesoglcea. Zeiss D. 



Oc. 2. 

 ,, 25. Modified ectoderm of the body-wall of Dendrqphyllia gracilis, showing the thickened walls of the 



ectodermic epithelium, mg., mesoglcea. n 2 , medium sized nematocysts, 0'028 millim. in 



length n 3 , large nematocysts, - 035 millim. in length. Zeiss. Imm. -jV-. Comp. Oc. 4. 

 26. Nematocysts of D. gracilis. Zeiss. Imm. T V. Comp. Oc. 4. 



26a. A spiral - 02-millim. tentacular nematocyst, its inner end prolonged into a fine nerve fibril. 

 ,, 26b. Nematocyst from the stomodajum or mesenterial filament. 

 ,, 26c. Developing nematocyst from the external ectoderm (see text). 

 26d. A ripe nematocyst from the external ectoderm. 

 26e. The same diagrammatically represented. 

 27. Four endoderm cells from a mesentery of D. gracilis, showing n, an endodermic nematocyst. 



m.p., muscular processes. Zeiss. 1mm. t V. Comp. Oc. 4. 



