CHAPTEE XXV 



THE SPECIAL SENSES 



289. Importance of the special senses. The means by 

 which animals become acquainted with the outer world 

 are the special senses, such as feeling, tasting, smelling, 

 hearing, and seeing. The behavior of animals with regard 

 to their surroundings, with regard to all the world outside 

 of their own body, depends upon what they learn of this 

 outer world through the exercise of these special senses. 

 Habits are formed on the basis of experience or knowledge 

 of the outer world gained by the special senses, and the 

 development of the power to reason or to have sense de- 

 pends on their pre-existence. 



290. Difficulty of the study of the special senses. We are 

 accustomed to think of the organs of the special senses as 

 extremely complex parts of the body, and this is certainly 

 true in the case of the higher animals. In our own body 

 the ears and eyes are organs of most specialized and highly 

 developed condition. But we must not overlook the fact 

 that the animal kingdom is composed of creatures of widely 

 varying degrees of organization, and that in any considera- 

 tion of matters common to all animals those animals of 

 simplest and most lowly organization must be studied as 

 well as those of high development. The study of the spe- 

 cial senses presents two phases, namely, the study of the 

 structure of the organs of special sense, and the study of 

 the physiology of special sense that is, the functions of 

 these organs. It will be recognized that in the study of 

 how other animals feel and taste and smell and hear and 



371 



