110 



Fig. 13. The oral ring of a young specimen of Br. coronata, magnified, viewed from above. 



Fig. 14. Part of the same, more strongly mangnified, seen from the exterior side: 

 IV, wedge-plate. 



Fig. 15. Part of the oral ring of the same specimen, with the base of an arm in 

 natural connexion, viewed from above: iv, wedge-plate; r, dorsal marginal plates; x, the 

 circular rim preceding from the interior wall of the oral ring. 



Tab. Jfl 



Fig. 1. A part of the disc (a radial space) seen from below, strongly magnified. 

 The water-feet and the spines are removed, in order to expose the central parts of the 

 nervous system: a a, the circular nerve-commissure; 6, the radial nerve; c, insertion for 

 the water-feet; x, a recently formed germ of an arm, on which the terminal organ of sense 

 and the 2 I'ows of water-feet are already evidently traced. 



Fig. 2. The part of a radial nerve belonging to the disc, together with a part 

 of the circular commissure, isolated and viewed from the upper (interior) side: a, the longi- 

 tudinal septum which divides the radial blood-sinus. 



Fig. 3. The same vieved from the side: a, the septum. 



Fig. 4. A piece of a radial nerve from the basal part of an arm, shewing 2 of the 

 enlargements that correspond to the water-feet, viewed from above: a, the septum. 



Fig. .5. Another piece with 3 enlargements viewed from below. 



Fig. 6. The dorsal skin of the disc, viewed from the inner side, with the interior 

 parts attached, chiefly to shew the complicated arrangement of the ligaments by which the 

 stomach and the radial cffica are fixed: a, the secretory apparatus; A, the so-called „heart"; 

 s, the stone-canal. 



Fig. 7. The madreporic body viewed from above, magnified. 



Fig. 8. The „heart" isolated and viewed from the side. 



Fig. 9. A piece of the skin of the same, more strongly magnified, shewing the 

 reticulated muscular fibres. 



Fig. 10. Cells in the skin of the „heart", very strongly magnified. 



Fig. 11. A recently formed germ of an arm, magnified, viewed from above: a, the 

 terminal organ of sense. 



Fig. 12. The same viewed from below: a, the terminal organ of sense; h, the 

 enlargement of the radial nerve at the base of this organ; n, the radial nerve; tv, rudi- 

 ments of the water-feet. 



Fig. 13. Another germ of an arm, treated with a solution of potash to shew the 

 interior skeleton (s) forming itself, seen from the right side: p, nascent furrow-spines; 



