112 ' DR. WILSON ON THE NERVOUS SYSTEM OF THE ASTERID^. 



cells of the cone become elongated towards the apex ; but in tliis species I could observe 

 no change in their form from base to apex. Several of these were lengthened ; but this was 

 evidently the result of injury. On the addition of nitric acid, the vermilion of the cells 

 becomes first purple, then passing rapidly into blue and brown, at last disappears altogether, 

 leaving only the outline of the cone with the unaltered lens at the base. By reflected 

 light the individual eyes appear as opake funnel-shaped red masses, with a dark pit-like 

 centre at the base. 



Although Dr. Haeckel mentions his having seen nerve-cells and filaments covering the 

 optic bulb, he could not detect the connexion between the cells and the filaments, nor of 

 the latter with the individual eyes. In the Solctster, without any reagent, the nerve-cells 

 may occasionally be distinctly seen, lying above the bulb and sending filaments to the 

 individual eyes*. I have, in several specimens, traced these filaments to the apices of 

 the cones, which they entered ; their ultimate termination, however, still remains unde- 

 cided. Many of these cells are bipolar, one pole being connected with a cone, and the 

 other passing longitudinally towards the proximal end of the cord. What the medium 

 may be which occupies the space from the apex of the cone to the back of the lens, is as 

 yet doubtful, though certainly it is not filled with pigment-cells. The intermediate matrix, 

 within which the cones are imbedded, consists of granides at the base and centre of the 

 bulb (i. e. that part nearest the nerve-cells), — these granules becoming smaller the closer 

 they approach the circumference, so that around the bases of the cones it is finely 

 molecular. 



The bulb is covered by a transparent homogeneous cornea, whose epithelium consists 

 of very minute transparent polygonal cells t- That it is a modification of the integument, 

 is easily demonstrable by tracing, in profile, the rather opake granular skin along the 

 cord, and noticing, at the base of the bulb, its sudden change to the transparent cornea, 

 to be continued as such over the eye-spot +. 



The curious foot-like projection, extending beyond the oj)tic bulb, is comparatively 

 small and short in the Solaster §. It was only by careful dissection that I was enabled 

 to discover it, as it cannot well be seen when the animal is moving, owing to the bunches of 

 terminal spines, which project considerably beyond it. Probably the large size and mobi- 

 lity of the optic peduncle may account for the poor development of this organ in the 

 Solaster. As we find it well marked in Uraster rubens, I will describe it more minutely 

 when treating of the latter. From the nerve-cells lying at the base of the optic bulb some 

 filaments pass to the roots of this tactile organ. 



The ganglionic enlargement found at the beginning of the ambulacral cord is only 

 small in the Solaster\\. The difficulty experienced in removing it for examination has 

 prevented my detecting, as yet, nerve-cells in its structure. The same arrangement which 

 guards the ambulacral cord also protects the ganglion. 



The interambulacral cord {/), exceedingly thin and delicate, runs close by the side of 

 a calcareous mass {d), the free lower surface of which is convex, and generally supports 

 twelve club-shaped spines. These masses consist of two pieces placed in juxtaposition, 

 and each having six spines. They are modifications of those already described as sup- 



* Plate Xni. fig. 1 1 . t IlJ'd- fig- 7. c&h. J Ibid. fig. 4. § Ibid. fig. O.d. || Ibid. fig. 3. e. 



