114 ZOOLOGY 



146. Special Adaptations to the Inorganic Environment. — 



These embrace such special structural devices as hair, feathers, 

 the blubber of whales, which enable the body to maintain its 

 temperature despite the condition of the medium. The habits 

 of burrowing and hibernation, the winter migrations of many 

 animals, especially birds, are examples of instinctive adaptation 

 to cold and to food supply. The same end is obtained by man 

 by artificial clothing, by houses, and by the use of fire which has 

 been one of the most important instruments in his progress. 

 Rotifers, infusoria, and some other animals have become cap- 

 able of retaining life during thorough drying, and of resuming 

 activity on the return of moisture. Adaptations to locomotion 

 in different media, earth, air, and water ; to climbing ; to station- 

 ary life, belong to this group. These are only a few of the many 

 instances of adaptations of organisms to the materials and the 

 forces about them. It is easy to see that some of the adapta- 

 tions are of life and death importance, and without them the 

 species would become extinct. It has been argued that these 

 qualities of the organism arise in a way something like this: 

 owing to the irritability of all protoplasm, the prevalent external 

 factors as heat, light, gravity, moisture, and chemically active 

 substances must produce some change, — that is, some response 

 on the part of the organism. Through internal, hereditary 

 causes different animals respond with different degrees of suit- 

 ability to these conditions. Those organisms in which the 

 response is not in accordance with the best adjustment to the 

 special environment are less likely to survive in the struggle for 

 existence. Those which do survive and propagate their kind 

 because they are so endowed as to make favorable responses to 

 these stimuli are, by reason of these facts, more and more likely 

 in succeeding generations to possess and to develop those 

 structures and behavior which suit them to their surroundings. 



147. Practical Exercises. — Find other instances which seem to indicate adapta- 

 tion either in structure or habit to special features in the environment: as adapta- 

 tions to prevent undue evaporation in a dry climate; adaptations to warm condi- 

 tions; to varying temperature; to drouth; to the use of special plants as food; to 

 light; to gravity. Illustrate from observation and by library reference the types 

 of adaptations cited in the text above. Is the power of sleeping an adaptation of 

 any value? Among what animals is it found? Find instances in which originally 



