SHORES OF THE CLYDE AND FIRTH. 
61 
handling, I have >seen as many as a dozen at a time litter 
the floor of the tank. In their prowling life among -t the 
rocks and stones of the shore, they are continually liable to 
sustain injury and loss, a contingency carefully considered 
and amply provided for by the Divine Designer. Let us 
then see how the replacement is accomplished. 
Did they spring from the skin or shell they would 
certainly be found, from the size of a mere point piercing 
upwards through the skin, in their various stages of growth 
towards the adult state, but searching over the whole ball 
of the shell, no young spine can be found beneath a 
considerable size and a well-defined form. It cannot be 
that Nature abruptly shoots them forth at once to the 
height and perfect condition we find them in. They must 
have a beginning and process of development ; and this let 
us now endeavour to trace. With the assistance of a lens, 
a numerous host of small white stalks, from the thickness 
of the finest cotton twist to that of the most delicately- 
produced silken thread, are discovered springing from the 
skin in the interstices of the spines, also waving about in all 
directions. After long and careful study, these, I am 
inclined to believe, are the young spines in process of 
development, and if the larger ones are easily destroyed, 
SPINE AND PIVOT. 
E 
