The _Graptolites_ (Gr. _grapho_, I write; _lithos_, stone) were
so named by Linnaeus, from the resemblance of some of them to
written or pencilled marks upon the stone, though the great
naturalist himself did not believe them to be true fossils at
all. They occur as linear or leaf-like bodies, sometimes simple,
sometimes compound and branched; and no doubt whatever can be
entertained as to their being the skeletons of composite organisms,
or colonies of semi-independent animals united together by a common
fleshy trunk, similar to what is observed in the colonies of the
existing Sea-firs (Sertularians). This fleshy trunk or common
stem of the colony was protected by a delicate horny sheath, and
it gave origin to the little flower-like "polypites," which
constituted the active element of the whole assemblage. These
semi-independent beings were, in turn, protected each by a little
horny cup or cell, directly connected with the common sheath
below, and terminating above in an opening through which the
polypite could protrude its tentacled head or could again withdraw
itself for safety. The entire skeleton, again, was usually, if
not universally, supported by a delicate horny rod or "axis,"
which appears to have been hollow, and which often protrudes to
a greater or less extent beyond one or both of the extremities
of the actual colony.
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