14 PHILOSOPHY OF ZOOLOGY. 
when the muscular fibre appears to be equally susceptible 
of irritation, when the nerves are no longer visible to our 
senses, as when they are ageregated into perceptible fila- 
ments, we are disposed to consider the quality as resident 
in the fibre itself. And this opinion is confirmed, when the 
attention is directed to the irritability of the vegetable 
tribes. In this department of the organized kingdom, the 
existence of nerves has not been demonstrated, nor even 
rendered probable; yet the expansions and contractions 
which vegetable fibres exhibit upon the application of sti- 
mulants, indicate an irritability the same in kind with that 
of animals, although its effects are not so rapidly displayed, 
at the same time that they point out the place of its resi- 
dence. 
M. Lamark, in the introduction to his valuable work, 
‘¢ Histoire Naturelle des Animaux sans Vertebres,” Paris, 
8vo 1815, vol. 1., refers some of the movements which are 
here considered as indicating the existence of irritability 
in plants, to the influence of the mechanical or chemical 
powers, and others, to what he terms vital orgasm. All 
these different actions, however, occur in connection with 
the vital principle, and their entire dependence on the laws 
of inorganic matter is a gratuitous assumption. With re- 
gard to this orgasm of plants, it is identical with the irrita- 
bility of animals, and seems to have been employed by this 
author as a convenient ambiguous term, to aid him in his 
peculiar views of systematical arrangement. 
3. PossessED oF 1nstrNct.— In the exercise of those 
various powers which produce and modify the size, shape, 
structure, composition and duration of organized bodies, 
there is a more immediate reference to the formation of the 
individual, as it exists unconnected with surrounding ob- 
jects. The power of irritability, on the other hand, forms 
a medium of communication not only with the different 
