THE ANATOMY OF THE MADREPOKAR1A. 
597 
Fig. 11. — Transverse section through part of a mesentery, to show the 
mesodermal pleatings on which lie the muscles. 
Fig. 12. — Transverse section of an acontium of Flabellum. 
Fig. a. Transverse diagrammatic section of Caryophyllia (after v. Koch) . 
a. Septa, b. Mesenteries. 
Fig. b. Similar section through Caryophyllia, in a lower plane than a 
(after v. Koch), a. Septa, b'. Central, b". Peripheral parts of the 
mesentery, c. Costae, th. Theca. 
Fig. 13. — Diagram of a longitudinal section of Rhodopsammia, considerably 
shortened in the longer axis ; the right half of the figure taken along the 
lines c. c. in Figs. 14 and 15, i. e. in an exoccele ; the left along the lines d. d. 
in the same figures, and therefore cutting through a septum and a tentacle. 
c. Cut edge of external body-wall. d. Cut edge of tissues clothing theca and 
columella. B. Tissue clothing the entoseptum, which is seen projecting from 
behind the mesentery. On the left side the inner face of a mesentery (m) 
is seen similarly projecting from behind the septum. The costae being in this 
form rows of spines, appear as projections in both transverse (Fig. 14) a 
longitudinal (Fig. 13) sections. 
Fig. 14. — Transverse section of half of the calyx of Rhodopsammia, along 
the plane a. Fig. 13 (camera drawing). The numerals 1, 2, 3 are placed in 
the entocceles formed by a pair of mesenteries of those orders. Complete 
systems, 1, 3, 2, 3, 1, are only found in the region of the directives. The 
dashed numerals, 1', 2', 3', are placed in the external chambers which corre- 
spond to the entocoeles. ext. b. w. External body-wall. Corallum deep black, 
soft tissues in lighter black lines. 
Fig. 15. — Similar section along the plane b, Fig. 13. The septa have fused 
into the columella, and are numbered 1, 2, 3, according to their orders. 
/. Cavity filled with sponge spicules, y. Line of tissue which may belong to 
the polyp. 
Fig. 16. — Mesenterial filament of Rhodopsammia in transverse section. 
Fig. 17. — Fart of Fig. 14, enlarged to show the relations of the three 
body-layers. Mesoderm black, corallum grey. c. Thecal canal system in 
transverse section. c\ External chambers, corresponding to exocceles and 
entocceles, in each of which lies a costa. 
Fig. 18. — Part of the thecal canal system of Rhodopsammia, after removal 
of the corallum by decalcification. 
Figs. 19, 20, and 21.— Diagrams of the relations of a complete system of 
septa of Rhodopsammia at different heights. The numerals are placed at the 
bases of the entosepta. 
Fig. 22. — Calyx of Rhodopsammia, viewed from above. From a specimen 
in the British Museum. 
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VOL. XXV. NEW SER. 
