SHORES OF THE CLYDE AND FIRTH. 
55 
of the growth of this shell will be plainly understood. He 
says each of these symmetrical pieces of shell, which he 
numbers at only 600, is enveloped in a layer of living flesh, 
a vascular tissue of exceeding thinness, which passes up 
between the joints, where one meets another on every side ; 
and not only so, but actually spreads itself over the whole 
exterior surface. This being so, the glands of the inventing 
fleshy tissue secrete lime from the sea water, which holds 
it in solution, and constantly deposit it after a determinate 
and orderly pattern on every part of the surface of each 
shelly piece ; the inner face, the outer face, and each 
angle of the polyhedron grow together, and all so evenly, 
that while the dimensions increase both of thickness and 
superficies, the form characteristic of that individual piece 
is maintained with immutable mathematical precision. 
Thus, the volume and capacity of the box grow with the 
growth of the individual segments, and it ever keeps the 
globose shape at first imposed upon it. By this theory, 
which holds the credence of well authenticated facts, 
this fleshy tissue is exalted to the high position of being 
from first to last the sole constructor of this wonderful 
shell ; in other words, it is labourer, tradesman, and 
architect all rolled into one. At the risk of being 
designated presumptuous, or having the ire of an offended 
F.R.S. brought down upon my devoted head, I hereby 
humbly beg to intrude my disbelief in the theory, and say 
that it is not at all the true solution. 
That the glands of the investing fleshy tissue, through 
another agency, do " secrete lime from the sea water which 
holds it in solution," I hold to be perfectly correct, but 
they lack the power or force in themselves of depositing 
secretions on portions where they cannot reach, and actually, 
though covering over, do not even touch, and that is a by 
