122 DR. WILSON ON THE NERVOUS SYSTEM OF THE ASTERID^. 



cc. nuclear or cellule- like bodies lying immediately beneath the cuticle [d) and connected to 



the fibrils. 

 Fig. 3. Distal end of a ray, its ventral aspect, a. ambulacral cord, lying between two rows of suckers 



{a' a'), and ending in the optic bulb {b) : the cones are arranged transversely, and mark off very 



distinctly a clear triangular space, situated at the free end (c), and having no eyes. /. tactile 



organ partly concealed by terminal rows of spines, which form a protective whorl {ff). 

 Fio-. 4. Diagrammatic view of perioral skeleton, a a. first pair of ambulacral plates, b b. spine-bearing 



pieces, being modifications of that marked e in fig. 1, c. intermediate piece connecting the 



spine-bearing mass to vertebral plates, d. ambulacral ganglion lying below inferior muscle. 



e. interambulacral nerve-cord, passing above the spine-bearing masses, and on a level with the 



ligament connecting the intermediate pieces (c c), ff. integument. 

 Fio-. 5. Individual eyes. a. bird's-eye view, showing the lens partly covered by the iris-like ring; 



b. profile of the same, exhibiting its conical form ; c. the lens lying imbedded at the base ; 



d. nerve-fibre entering its apex. 

 Fig. G. Profile of optic bulb in situ. Its outline is slightly convex. Between it and the skeleton lies a 



mass of nerve-cells (a), which send filaments to the cones (b b) and tactile organ (c). 



Uraster rubens. 



Fig. 7- Transverse section of ambulacral groove, a a. vertebral plates; a .r. fulcrum ; c c. tubercles 

 for inferior muscle ; c' c'. grooves, probably for the reception of the branch from water- 

 vessel (6) to vesicles {i i) ; d. superior muscle ; e. calcareous mass, supporting vertebral 

 plates, and bearing two long sharp spines, which have at their apices radiating spinules ; e'. a 

 second piece, giving articulation to three short thick spines, connected to the other by the inter- 

 mediate piece (/) ; ff. ambulacral nerve-cells and their filaments ; h. integumentary covering ; 

 k k. suckers. 



Fig. 8. Diagi-am of perioral skeleton, a a. vertebral plates; b b. spine-bearing masses, each homo- 

 logous to that marked e in fig. *J ; c. ambulacral ganglionic cells lying below the inferior 

 muscle ; d. interambulacral nerve-cord passing between the lower ends of vertebral plates and 

 the spine-bearing pieces ; e. integument. 



Fig. 9. Transverse section of ambulacral groove of a specimen treated with carmine ; the nerve-cells 

 and their filaments are rendered very distinct by the colouring matter, a. some of these more 

 highly magnified, showing the nucleus of the cell and central axis of the fibre highly tinged 

 by the carmine. 



Fig. 10. Distal end of ray (its ambulacral aspect), showing the eye and tactile organ hi situ. a. nerve- 

 cord ; b. optic bulb ; c. tactile organ, greatly concealed by the spines which spring from 

 the lateral plates {dd). 



Fig. 11. Diagram of the protective apparatus of the eye and tactile organ. a,b,c, d. first, second, third, 

 and central rows of spines as seen when the eye is exposed ; E. the same when covering and 

 protecting the eye-bulb and tactile organ. 



Tab. XV. 



Uraster rubens (continued). 



Fig. 1. Nerve-cells and filaments from ambulacral cord of a specimen treated with alcohol and acetic acid. 



Fig. 2. Other nerve-cells from the same specimen, highly magnified. Their fibre shows the double con- 

 tour distinctly. 



Fig. 3. Profile of optic bulb and tactile organ in situ, exhibiting the saddle-shaped outline, a. tactile 

 organ ; b. its cavity, seen to pass towards the termination of the water-canal (c). 



