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



first sight as if tuberculated* ; and it is owing to the shortness of these spines that the 

 bulb (i) aiid the tactile organ (/) are very easily seen when the animal is in motion. 

 The optic bulb, though having no special protective spines, is nevertheless covered in 

 by those connected to the adjoining vertebrae. These spines are very much tinged, on that 

 side next to the eye-spot, by pigment of the same colour as that of the eye itself. 



The bulb is not so distinctly pedunculated, nor so free from the tactile organs, to wliich 

 it is connected somewhat higher up than its rootf. It is altogether much smaller in size 

 than that of the Solaster, and its longitudinal diameter proportionately greater than its 

 transverse ; so that its shape is more elongated %. In profile it is generally slightly convex 

 in outline, sometimes almost flat, and occasionally even saddle-shaped. This variable- 

 ness in its contour seems to be dependent upon the position of the tactile organ on which 

 it rests. 



A bird's-eye view of the sm'face of the bulb shows the arrangement of the individual 

 eyes to vary, much in the same manner as in the Solaster ; they seem, however, to be 

 principally distributed in obliquely transverse lines diverging from a mesial one. The 

 longitudinal division of the bulb into two lateral portions is well indicated by the central 

 series of individual eyes. The two last divergent lines of cones, nearest the free end of the 

 bulb, bound a clear triangular portion studded here and there with pigment-points. 



The individual cones, smaller than those of the other species, all diverge from a line 

 which bisects longitudinally the ocular mass. The pigment is more of a carmine-red, 

 and the nucleated cells containing it are also smaller and more densely grouped around 

 the cone §. Nitric acid produces effects similar to those already described. Tlie lens (c) 

 imbedded in the base of each cone is not so well seen in the Cribella, owing to the ii-is-Mke 

 ring greatly concealing it. It has the same appearance as in the Solaster, difi'ering only 

 in the smallness of its size. Professor Goodsir, years ago, described these eyes as " con- 

 sisting of a red cushion with pits on its surface ||." This appearance is especially evident 

 when the bulb is examined by reflected light. 



Nerve-filaments pass into the apices of some of the cones ; but I have not been able to 

 trace them to any of the cells ^. The high colour of the integument around the bulb 

 prevents the subcutaneous structures being seen clearly through it. Eor the same reason, 

 nothing could be distinctly made out regarding the matrix surrounding the cones. 



The tactile organ is very long, and projects far beyond the terminal cluster of short 

 spines situated at the ray-point**. It is conical, with a blunted extremity, not very 

 transparent, and orange-brown in colour. If a young specimen be placed in shallow 

 water and watched through a lens whilst it is moving, the tactile organ will be seen pro- 

 truded from the curved end of the ray, and bearing, on its lower aspect, the eye-spot. By 

 means of it the optic bulb can be turned either laterally or towards the centre of the body. 

 As the bulb is moved from one side to the other, it is very beautiful to notice the lens 

 of each individual eye reflecting, very brightly, for a moment the pencils of light, and 

 then disappearing as another is substituted. The animal never uses tliis tentacle as a 

 foot. When the ray approaches an obstacle the tactile organ either curves inwards over 



* Plate XIV. fig. 3. t Ibid. fig. G. J Ibid. figs. 3 & 6. § Ibid. fig. 5. 



II Forbes, E., History of British Starfishes. % Plate XIV. fig. 6. a. ** Ibid. fig. S.f, and 6. c. 



