FUNCTION AND STRUCTURE YY 



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. 



