THE VERTEBRATES AND THEIR ENVIRONMENT 



27 



to the order of np,ture, even if that were desirable. It is only pos- 

 sible to go forward to an increasing control. If men are to live 

 herded together in cities, to traffic up and down the seas, to cul- 

 tivate the soil, and to solve the problems of increasing population, it 

 must be through an ever more effective control of their surround- 

 ings. The material problems of human beings are, biologically 

 speaking, the problems of an organism that is struggling to control 

 an environment from which much has been secured, but from 

 which much remains to be wrested if the species is to be made 

 safe in its present position or to reach higher levels. Because 

 scientific knowledge is the key to this situation, science assumes 

 an increasing importance in the life of mankind. 



The Vertebrates and their Environment 



Habits, Habitat, and Distribution. — Having examined the 

 natural history of the frog as a representative vertebrate, we 



Fig. 13. — The climbing perch, a fish that can leave the water and travel for 

 some distance on land by means of an adaptation for storing water above 



the gills. 



The fish on land and head dissected to show structure of gill region; 6 a., first branchial 

 arch; l.o., labyrinthiform organ; op., operculum; sb.c, suprabranchial cavity. (Left, cour- 

 tesy of Nature Magazine; right, from The Cambridge Natural History, copyright, 1920, by 

 Macmillan and Co., Ltd., reprinted by permission.) 



may next consider the natural history of the vertebrates as a 

 diversified group of animals. In connection with the classifi- 

 tion of vertebrate animals (p. 36), reference will be made to 

 the habits and habitats of the several types. The fishes (Fig. 

 1 C, D, E) are aquatic, and breathe by means of gills, although 

 certain species are adapted for brief excursions from the water. 

 Among these may be mentioned the climbing perch (Fig. 13), 



