324 GILBERT C. BOURNE. 



Fig. 11. Ad naiuram. — Two contiguous mesenteries not belonging to the 

 same pair, from an adult Fungia, showing their tendency to fuse together in 

 old specimens. Lettering as before. 



Fig. 12. Ad naturam. — Section through an acontium, showing the dendritic 

 branching of the mesoderm in the acontium, the large nematocysts cd., and 

 the gland-cells gd. 



Fig. 13. — Diagrammatic horizontal section through the corallum and soft 

 parts of Fungia deutata. The corallum is shaded, the mesogloea is repre- 

 sented by a black line. The calycoblasts are omitted for simplicity's sake. 

 The septa are seen to lie in the entocceles, the ccelenteron being broken up 

 by the synapticula into a number of parallel tubes, in each of which are seen 

 the mesogloea tliickeuings x, which give attachment to the vertical muscle- 

 fibres. The acontia of the lower orders of mesenteries are seen coiled up in 

 the Cffilenteron. mt. Mesenteries, syn. Synapticula. 



Fig. 14. Ad naturam. — Section through the body wall of F. dentata. 

 ed. Endoderm. m. Mesogloea. ec. Ectoderm, n. Interstitial cells. 



Fig. 15. — Diagrammatic vertical section through the peripheral part of F. 

 dentata, ec. p. Ectoderm of the peristome, ec. b. Ectoderm of the base. 

 The shading and lettering as in Fig. 13. th. Theca. ex. Exocoele. ent. Ento- 

 ccele external to theca. 



Fig. 16. — Diagram illustrating the relations of the coelenteron to the 

 corallum. The drawing may be considered as a cast of all the cavities lined 

 by endoderm. At sp. are shown the spaces occupied by the septa, by which 

 the body is broken up into a number of wedge-shaped masses. The rows of 

 parallel elongate perforations show the position of the synapticula. At cwl. is 

 seen that part of the body cavity which lies outside the perforate theca. 

 th. Perforations for theca. syn. Perforations for synapticula. 



Fig. 17. — A portion of the skeletotrophic investment higlily magnified. 

 ed. Endoderm. m. Mesogloea. cy. Calycoblasts 



