202 THE FITNESS OF THE ENVIRONMENT 



H H H H 



C C C H C 



HC C CH HC C - C - C CH 



I I! I , I II I I II 



HC C CH HC CH H HC CH 



x/\z x/ x/ 



c c c c 



H H H H 



It is quite impossible briefly to indicate, 

 still less to give an adequate idea of the 

 bewildering diversity and complexity of the 

 known hydrocarbons. They exist by the 

 hundreds, and there are certainly countless 

 thousands of possible stable bodies made up 

 of carbon and hydrogen alone. 



C 



COMPOUNDS OF CARBON, HYDROGEN, AND OXYGEN 



With the addition of oxygen, the variety and 

 number of known and of possible substances 

 is still further multiplied. Oxygen may enter 

 into the following types of union with carbon 

 and hydrogen in organic compounds : — 



= C-0-H, = C-0-C=, =C=0. 



Alone or in combination, these groups yield 

 a great variety of important classes of com- 

 pounds. Representing a group or radical 

 consisting of carbon and hydrogen alone by 



