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 aggregated into perceptible fila- 

 ments, we are disposed to consider the quality as resident 

 in the fibre itself. And this opinion is confirmed, whei} 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 Naturelie des Animaux sans Vertebras," Paris, 

 8vo 1815, vol. i., 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 INSTINCT. 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 



