168 



FOUNDATIONS OF BIOLOGY 



mechanism necessitated by abandoning the aquatic for the 

 terrestrial mode of life, with the consequent dependence on 



FIG. 93. Diagram of paths of absorbed food from the digestive tract. 

 Proteins and carbohydrates by] veins (in solid black) ; Fats by lymphatics 

 (dotted). (From Conn and Budington.) 



the free oxygen of the atmosphere instead of that dissolved 

 in the water. 



B. RESPIRATION 



As we have seen, the essential factor of respiration is an 

 interchange of gases between protoplasm and the environ- 



