CONSTRUCTION OF SHELLS. 17 
for the endless diversity of shades and colours, vary- 
ing from the sober coating of the garden snail, to the 
delicate and glowing tints which are diffused over 
some of the finer species, in the infinite profusion of 
undulations, clouds, spots, bands, and reticulated 
figures, with which these admirable architects enrich 
the walls of their beautiful receptacles? The means 
of producing them must be sought for in the animals 
themselves. Their necks are furnished with pores 
replete with colouring fluid, which blends insensibly 
with the calcareous exudation already noticed, and 
thus occasions that exquisite variety in their testa- 
eeous coverings, which art attempts to emulate, but 
can never fully equal. 
Thus far is the result of observation and experi- 
ment. It now remains to account for the extra- 
ordinary fact, that the stony exudations of testaceous 
animals condense only on those parts where they 
are essential to their welfare. But here investigation 
ends—the microscope has done its office. It seems 
as if maternal nature delighted to baffle the wisdom 
of her sons; and to say to the proud assertors of the 
sufficiency of human reason for comprehending the 
mysteries of creation and of Providence, ‘‘ Thus far 
can you go, and no further ;” even in the formation 
of a shell, or its insignificant inhabitant, your arro- 
gant pretensions are completely humbled. 
c 
