viii TABLE OF CONTENTS 



CHAP. PAOB 



IV. General Principles concerning Animals - - - 47 



The actions of animals only take place by means of movements 

 that are stimulated, and not transmitted from without. Irri- 

 tability is a faculty which they all possess, and is not found except 

 in animals : it is the source of their actions. It is not true that 

 all animals possess feeling, nor the faculty of carrying out acts 

 of will. 



V. On the True Arrangement and Classification of 



Animals 56 



That animals may be arranged, as regards their larger groups, 

 in a series which exhibits a gradually increasing complexity of 

 organisation ; that the knowledge of the affinities between the 

 various animals is our only guide in determining this series, and 

 that the use of this method dispenses with arbitrary judgments ; 

 lastly, that the number of the lines of demarcation, by which 

 classes are established, has to be increased in correspondence with 

 our knowledge of the different systems of organisation, so that the 

 series now presents fourteen distinct classes, of great service in 

 the study of animals. 



VI. Degradation and Simplification of Organisation, 

 from one Extremity to the other of the Ani- 

 mal Chain, proceeding from the most complex 



TO THE simplest - - 68 



That it is a positive fact that on following the animal chain in 

 the usual direction from the most perfect to the most imperfect 

 animals, we observe an increasing degradation and simplification 

 of organisation ; that, consequently on traversing the animal 

 scale in the opposite direction, that is to say, in the same order 

 as Nature's, we shall find an increasing complexity in the organisa- 

 tion of animals, a complexity which would advance with evenness 

 and regularity, if the environmental conditions, mode of life, etc., 

 did not occasion many anomalies in it. 



VII. Of the Influence of the Environment on the 

 Activities and Habits of Animals, and the 

 Influence of the Activities and Habits of these 

 Living Bodies in modifying their Organisation 

 and Structure - ■ 106 



How the environment acts upon the organisation, general form 

 and structure of animals ; how changes subsequently occurring 

 in their environment, mode of life, etc., involve corresponding 

 changes in the activities of animals ; lastly, how a change in the 

 activities, which has become permanent, involves on the one 

 hand more frequent use of certain parts of the animal, thus 

 developing and enlarging them proportionally ; while, on the 

 other hand, this same change diminishes and sometimes abolishes 



