CHAPTER XIII 
THE SPECIAL SENSES 
116. 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. 
11%. 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 cars 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 
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