THE ANIMAL ORGANISM 41 



supply of energy to carry it through the winter. Late in the 

 autumn the frog buries itself in mud below the frost line and 

 passes the cold months in a state of suspended animation. 

 Respiration is reduced to a minimum and is confined to the skin. 

 The body temperature drops until it is only slightly above the 

 temperature of the ground. Metabolic activity is displayed in 

 the activity involved in producing a circulation of the blood and 

 in the development of the eggs and spermatozoa. When the 

 frog emerges from hibernation in the spring it still possesses 

 sufficient reserves of energy to complete spawning before resum- 

 ing feeding. 



The foregoing is a summarized statement of the general plan 

 of the structural and of the functional activities of the frog. 

 In the following chapters the discussion of organization is con- 

 tinued by comparing organ systems of selected animals, both 

 structurally and functionally, using the frog as the basic form, 

 for the purpose of obtaining a bird's-eye view of the conditions 

 found in as many different types of animals as can be conven- 

 iently studied. It must be remembered, however, that the organ- 

 ism as a whole is the real unit in living nature and that the 

 comparison of organ systems is a comparison of parts of the 

 organism unit. The alternative to such a plan is to consider only 

 entire organisms, a procedure that is entirely sound but one 

 which limits the scope, if the time available for study is to be 

 considered. However, a basis for the appreciation of the com- 

 parison of organ systems is provided by the laboratory work in 

 which a number of selected forms are studied as whole organisms. 

 With the laboratory experience as a background, the comparative 

 study of organ systems serves to bridge the gaps left by the 

 laboratory programs and offers a practical method of securing a 

 general survey of the field in the shortest time. 



