SHORES OF THE CLYDE AND FIRTH. 57 
always place the power of resistance, leverage, and motion 
in the proper place. If, indeed, the tissue was the 
constructor of the spines, it would require to reach the top 
in order to lay down the deposits required for growth and 
strength, like the bark of a tree conveying the sap upwards, 
and in that case we would have a skin-bound motionless 
spine as unable to move as the mast of a ship bound down 
to her bulwark by the shrouds. Turning from the spines 
for a moment, with the assistance of a lens, a great army of 
little jelly-like arms, far more numerous than the spines 
themselves, are seen also waving about in all directions. 
The head of these is designated by some as " threbble- 
headecl pincers," or forceps, but they are of two distinct 
patterns — one having the three sections of the branches 
very much like the shape of the leaf of the shamrock; while 
the other, when stretched out to its full length, is a 
branched web, with the branches stretching out in a 
triangular fashion, and uniting in a curve near the centre. 
These are classically called 
PEDICELLARI^, 
and at one time were supposed to be parasites living upon 
the skin of the creature, but are now believed to be distinct 
organs ; but their work is unknown. Some supposed them 
to multiply the means of progression ; others, that they 
acted as the creature's police, in expelling intruders that 
entered in amongst the spines ; others, again, that they 
acted in laying hold of nervous matter, which was conveyed 
from one to another till it reached the mouth. The 
branches are something of a silicate nature, armed on the 
edges with a row of teeth, and from their extremities to the 
centre of the throat are intersected by numerous little cells. 
In the hither and thither motion of these appendages 
