536 VERTEBRATE LIFE AND ORGANIZATION 



l,c (ligisttci? Wliat controls the secretion of the digestive enzymes required? What 

 would happc-n to the products of digestion? 



8. What are the functions of the large intestine? 



9. How tioes defecation differ from excretion? What excretory products may be present 

 in the feces? 



10. List the functions of the liver. 



11. How do the gills of fishes fulfill the requirements of respiratory membranes? How is 

 water circulated across them? 



12. What exchanges between the body and the environment occur in the gills of fishes? 



13. In what group of vertebrates, and under what environmental conditions, did lungs 

 first evolve? 



14. In what respects is the external respiration of amphibians poorly adapted to the 

 terrestrial environment? How has this been improved in higher tetrapods? 



15. How is inspired air conditioned in mammals? Why is this more important in a mam- 

 mal than in a frog? 



16. \Vhy is it that alveolar air differs in composition from atmospheric air? Of what sig- 

 nificance is this? 



17. What causes the increase in the rate and depth of breathing during exercise? Why is 

 such an increase necessary? 



Supplementary Reading 



The references cited at the end of Chapter 25 also apply to this chapter. Interesting 

 accounts of the discovery of the digestive and respiratory processes can be found in Fulton, 

 Selected Readings in the History of Physiology. Guyton's Textbook of Medical Physiology 

 has an excellent chapter on the fascinating problems of respiration in deep-sea diving 

 and in aviation. Respiratory adaptations to deserts and mountains are considered in Dill's 

 Life, Heat, and Altitude. 



