And, so far as the conditions of the
manifestation of the phenomena 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 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. In the highest, on the contrary, a great number
of parts combine to perform each function, each part doing its allotted
share of the work with great accuracy and efficiency, but being useless
for any other purpose.
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