I 28 ZOOLOGY. 



in the waters of hot springs. Such must have been the way 

 in which other animals were changed from the marine to the 

 fresh-water habit, since all fresh-water animals are believed to 

 have been derived from marine forms. 



Similarly, in the history of any species those individuals 

 which respond in suitable or advantageous ways to the stimuli 

 brought to bear on them are selected from generation to gen- 

 eration in preference to those not so responding, and in the 

 course of time certain modes of action become characteristic 

 of the species, even without the necessity of individual ex- 

 perience. In other words the protoplasm has become so modi- 

 fied in a series of generations that responses of a definite kind 

 may be expected of it, which cannot be looked upon as in- 

 dividually acquired habits. These are instincts and embrace 

 many of the most interesting activities which have been men- 

 tioned as characteristic of animals. The instincts of feeding, 

 mating, and the like are examples. If instincts are in conflict, 

 the stronger prevails. In this possibility of situations arising 

 in which the instincts are in conflict, or are unequal to a correct 

 solution, lies the advantage of intelligence and choice as adap- 

 tations whereby correct responses may be made to external 

 conditions. Of the utmost importance in the development of 

 intelligence is the introduction of imitation, of training, of 

 experience, of memory, factors more or less represented in 

 the activities of all the higher animals. It is necessary to re- 

 member that what we call intelligence does not arise suddenly 

 in the animal kingdom and is not confined to the highest ani- 

 mals. Many of the acts usually spoken of as instinctive are 

 not purely so, but are the results, in part, of imitation, parental 

 or social training, and individual experience, and are therefore 

 to be classed as intelligent. 



163. The Dispersal of Animals and the Formation of 

 Special Faunas. In section 1 36 we see that every point occu- 

 pied by the individuals of any species becomes, under natural 

 influences, a centre of distribution from which the species will 



