114 DR. WILSON ON THE NERVOUS SYSTEM OF THE ASTERID^ 
first sight as if tuber culated * ; and it is owing to the shortness of these spines that the 
bulb (b) and 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 which 
it is connected somewhat higher up than its root f . 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 t • 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 surface 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. The lens (c) 
imbedded in the base of each cone is not so well seen in the Cribella, owing to the iris-like 
ring greatly concealing it. It has the same appearance as in the Solaster, differing 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 this tentacle as a 
foot. When the ray approaches an obstacle the tactile organ either curves inwards over 
* Kate XIV. fig. 3. f Ibid. fig. 6. J 
|| Forbes, E., History of British Starfishes. f Plate XFS 
§ 
/ 
c. 
