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CHAPTER VII. 



THE SENSES OF ANIMALS. 



IT is part of the essential nature of an animal to be recep- 

 tive and responsive. " The forces of nature rain their 

 influence upon it ; and it reacts to their influence in certain 

 special ways. Other organisms surround it, compete with 

 it, contend with it, strive to prey upon it, and occasionally 

 lend it their aid. It has to adjust itself to this complex 

 environment. 



There are two kinds of organic response one more or 

 less permanent, the other temporary and transient. We 

 have already seen something of the former, by which the 

 tissues (the epidermis of the oarsman's hand, and the 

 muscles of his arm) respond to the call made upon them. 

 The response is here gradual, and the effects on the 

 organism more or less enduring. This, however, is not 

 the kind of response with which we have now to deal. 

 What we have now to consider is that rapid response, 

 transient, but of the utmost importance, by means of which 

 the organism directly answers to certain changes in the 

 environment by the performance of certain activities. The 

 parts specially set aside and adapted to receive special 

 modes of influence of the environment are the sense- 

 organs. We human folk get so much pleasure from and 

 through the employment of our sense-organs, that it is 

 important to remember that the primary object of the 

 process of reception of the influences from without was not 

 the aesthetic one of ministering to the enjoyment of life by 

 the recipient organism, but the essentially practical one of 

 enabling that organism to respond to these influences. In 



