230 THE NATURE-STUDY REVIEW [ 3 : 8-nov., .1907 



Thus, the fundamental structures of animals, or plants for that 

 matter, are simply answers to the demands of their business as 

 stipulated in this table. Differences in structure and habits, 

 therefore, are due largely to different methods of meeting these 

 necessities of life. A given organ, once established, frequently 

 fulfills more than one of these functions, but the point is that 

 these and only these occupations concern the animal. 



Much of the machinery of any animal is connected with the 

 prime necessity of obtaining food and drink. Unlike plants, 

 animals do not have their food at hand in soil or air. They must 

 seek for it. Thus have arisen the various types of legs, wings and 

 other organs of locomotion. Organs of locomotion alone would 

 be of little service to the animal, however, if it had nothing to 

 direct them; there must be a centre of control and this is pro- 

 vided ordinarily in the central nervous system. The animal 

 requires, moreover, some mechanism to give it knowledge of 

 objects at a distance, hence have arisen such structures as eyes 

 through which it receives information by means of light, ears for 

 sound, a nose for odors, etc. These organs may serve more than 

 one purpose, of course, when once established. They are, for 

 example, as necessary to herbivorous animals for escape from 

 being made food of as to aid them in finding their own food. 



When an animal once confronts its food, however, it must still 

 meet the difficulty of getting it into its body. The food is solid, 

 perhaps, and must be subdivided, or it is alive and must be killed 

 before the animal can use it. There must be some organ or 

 organs, therefore, such as mouth, trunk, claws, hands or the like 

 to serve in this capacity, and still modifications of these organs 

 or additional organs to grind or cut the food into small bits that 

 it may be passed on into the body to be digested. Such organs 

 range from the commonplace to the grotesque and their nature 

 depends very largely upon the character of the food ; it requires 

 different machinery for killing and rending flesh from that which 

 must serve for plucking grass or for grinding grain. 



Before leaving the subject of food it should be mentioned that 

 such structures as those for breathing and for the circulation of 

 the blood are concerned with nutrition no less certainly than the- 

 more evident organs of alimentation. The blood distributes 

 digested food to where it is needed in the different parts of the 

 body, and oxygen, which is obtained by breathing, must be 



