110 DR. WILSON ON THE NERVOUS SYSTEM OF THE ASTERID^E 
to determine if they go to the suckers. On examining, however, the feet while the animal 
is in motion, a delicate streak, more transparent than the surrounding structure, may he 
seen, which, prohably, is the nerve-filament given to it. 
In addition to the filaments already enumerated, very delicate fibres may be observed 
passing from the mass of cells towards the integument. I have not yet succeeded in 
tracing these to a cell ; but should they prove more than connective tissue, the fact would 
greatly support Professor Goodsir's hypothesis, « that the so-called unipolar nerve-cells 
are in reality multipolar, of which one pole is an ordinary nerve-fibre, while the others 
consist of much more delicate and slender fibrils *." There is no doubt that the skin 
of the Solaster is exceedingly sensitive— so much so, that gentle irritation of any part will 
cause the suckers to be extended and withdrawn in a rapid and irregular manner, whereas 
the slightest wound of the cord itself causes their instantaneous contraction. 
When the animal adducts its ambulacral plates, the integument covering the groove 
becomes folded into a ridge and carries some of the nerve-ceUs along with it, so that these 
appear to lie in the fold so formed. The ridge formed by the folded integument has a 
wavy outline given to it by the row of suckers on either side, and would indicate that the 
skin is not contractile f. By reflecting a portion of this fold, and spreading it carefully on a 
glass slide before examining it with the microscope, bipolar nerve-cells may often be seen. 
I have not as yet detected any in a vertical section. Their filaments run either obliquely 
outwards or in the direction of the cord. In a longitudinal section of the arm, made along 
centre of the nerve-cord, we occasionally succeed in obtaining a view of the loneitudi 
«, y^y, kjj. ti^v -i"" & 
nal arrangement of the cells. In such instances we often notice that they cluster somewhat 
more thickly opposite the intervertebral spaces, much in the same manner as the linearly 
arranged ganglia of some of the Articulate. Nerve-cells may be traced along the whole 
length of the cord, as far as the upper part of the bulbous enlargement of the eye-spot. 
The eye of the Solaster is situated on the under surface of a well-marked peduncle, which 
is connected by its root, not only to the cord, but also slightly to the base of the tactile organ, 
from which it projects J. It is very mobile, and may be seen, if the animal is examined 
with a lens whilst moving, to be, to a great extent, the means of turning the eye laterally, 
upwards, or downwards. These movements may be carefully watched in the Solaster, as 
its eye-bulb is comparatively large, free of protective spines, and well elevated on its 
peduncle. On turning up the ray so as to expose its ambulacral or ventral surface, and 
removing, with the assistance of a dissecting-microscope, all the suckers around the eye, 
tlie latter appears more or less cylindrical, with its longest diameter in the longitudinal 
direction §. ° 
The bulb rests partly on the inferior ligament, but mainly on two calcareous masses (e e) 
set swe by aide, being probably a coalescent condition of the ultimate vertebra (o e), thus 
united for protective purposes. These masses bear on then- ventral surfaces and distal 
^_ vTS! 6 r ° WS ° f SpiaeS ' corres P° nd i°S serially with those already described in 
connexion with the vertebral plates. These spines can be turned inwards by the animal, 
t Tbt foUUs l« CCtUreS °\ C ° m V™™ *T. by Prof. Goodsi, Summer of 1858. 
t Plat X , I r n " ' he tra,WerSe **» ° f *' — of CriMla oculata in Plate XIV. fi K . 1 . 
t s 
5 
