112 ZOOLOGY 



2. Competitive. 



(c) The predaceous habit: adaptations for offense 

 and defense. 



(d) Parasitism. 



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. 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 capable of retaining life during 

 thorough drying, and of resuming activity on the return of mois- 

 ture. Adaptations to locomotion in different media, earth, air, 

 and water; to climbing; to stationary 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 adaptations are of life and death 

 importance, and without them the species would become extinct. 

 It is believed 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. Those or- 

 ganisms 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 propa- 

 gate their kind because of their favorable responses to these 

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

 succeeding generations to possess those habits and structures 

 suiting 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 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 



