FUNCTION AND STRUCTURE vid 
of animals; others, like the weevils, feed on the hard, dry 
substance of seeds and grains; others, like the grasshop- 
pers and caterpillars, eat green leaves; and still others eat 
other insects. The alimentary canal of each of these kinds 
of insects differs more or less from that of the other kinds. 
The specialization of the alimentary canal depends then 
upon the necessity for a large food-digesting and absorbing 
surface, and on the complex treatment of the food. The 
character of this specialization in each case depends upon 
the special kind or quality of food taken by the animal in 
question. 
45. The mutual relation of function and structure—The 
structure of an animal depends upon the manner in which 
the life processes or functions of the animal are performed. 
If the functions are performed in a complex manner, the 
structure of the body is complex ; if the functions are per- 
formed in simple manner, the body will be simple in struc- 
ture. With the increase in degree of the division of labor 
among various parts of the body, there is an increase in 
definiteness and extent of differentiation of structure. 
Each part or organ of the body becomes more modified and 
better fitted to perform its own special function. A pecul- 
iar structural condition of any part of the body, or of the 
whole body of any animal, is not to be looked on as a freak 
of Nature, or as a wonder or marvel. Such a structure has 
a significance which may be sought for. The unusual 
structural condition is associated with some special habit 
or manner of performance of a function. Function and 
structure are always associated in Nature, and should always 
be associated in our study of Nature. 
