Judging from what we actually
know as to the structure of the Trilobites, and also from analogous
recent forms, it would seem that these ancient Crustaceans were
mud-haunting creatures, denizens of shallow seas, and affecting
the soft silt of the bottom rather than the clear water above.
Whenever muddy sediments are found in the Cambrian and Silurian
formations, there we are tolerably sure to find Trilobites, though
they are by no means absolutely wanting in limestones. They appear
to have crawled out upon the sea-bottom, or burrowed in the yielding
mud, with the soft under surface directed downwards; and it is
probable that they really derived their nutriment from the organic
matter contained in the ooze amongst which they lived. The vital
organs seem to have occupied the central lobe of the skeleton,
by which they were protected; and a series of delicate leaf-like
paddles, which probably served as respiratory organs, would appear
to have been carried on the under surface of the thorax. That
they had their enemies may be regarded as certain; but we have
no evidence that they were furnished with any offensive weapons,
or, indeed, with any means of defence beyond their hard crust,
and the power, possessed by so many of them, of rolling themselves
into a ball. An additional proof of the fact that they for the
most part crawled along the sea-bottom is found in the occurrence
of tracks and markings of various kinds, which can hardly be
ascribed to any other creatures with any show of probability.
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