LAMARCK'S THEORY OF DESCENT 



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category, being necessarily limited and always the 

 same in the same species, the inner feeling and, con- 

 sequently, the power of acting, always produces the 

 same actions. 



" It is not the same in animals which besides a 

 nervous system have a brain [the author meaning 

 the higher vertebrates], and which make compari- 

 sons, judgments, thoughts, etc. These same animals 

 control more or less their power of action according 

 to the degree of perfection of their brain ; and al- 

 though they are still strongly subjected to the results 

 of their habits, which have modified their structure, 

 they enjoy more or less freedom of the will, can 

 choose, and can vary their acts, or at least some of 

 them." 



Lamarck then treats of the consumption and ex- 

 haustion of the nervous fluid in the production of 

 animal movements, resulting in fatigue. 



He next occupies himself with the origin of the 

 inclination to the same actions, and of instinct in 

 animals. 



" The cause of the well-known phenomenon which 

 constrains almost all animals to always perform the 

 same acts, and that which gives rise in man to a pro- 

 pensity {penchant) to repeat every action, becoming 

 habitual, assuredly merits investigation. 



" The animals which are only ' sensible ' * — namely, 

 which possess no brain, cannot think, reason, or per- 

 form intelligent acts, and their perceptions being 

 often very confused — do not reason and can scarcely 

 vary their actions. They are, then, invariably bound 

 by habits. Thus the insects, which of all animals 

 endowed withfeeling have the least perfect nervous 



* Lamarck's division of Animaux sensibles comprises the insects, 

 arachnids, Crustacea, annelids, cirripedes, and molluscs. 



