Among the lower plants, it is the rule rather than the exception, that
contractility should be still more openly manifested at some periods of
their existence. The protoplasm of Algae and Fungi becomes, under many
circumstances, partially, or completely, freed from its woody case,
and exhibits movements of its whole mass, or is propelled by the
contractility of one, or more, hair-like prolongations of its body,
which are called vibratile cilia. And, so far as the conditions of the
manifestation of the phaenomena of contractility have yet been studied,
they are the same for the plant as for the animal. Heat and electric
shocks influence both, and in the same way, though it may be in
different degrees. It is by no means my intention to suggest that there
is no difference in faculty between the lowest plant and the highest, or
between plants and animals. But the difference between the powers of the
lowest plant, or animal, and those of the highest, is one of degree,
not of kind, and depends, as Milne-Edwards [97] long ago so well pointed
out, upon the extent to which the principle of the division of labour is
carried out in the living economy. In the lowest organism all parts
are competent to perform all functions, and one and the same portion of
protoplasm may successfully take on the function of feeding, moving, or
reproducing apparatus.
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