200 THE FITNESS OF THE ENVIRONMENT 



has ever failed who has set out with skill, 

 a good plan, and suitable starting materials, 

 to prepare such a body. 



The number and variety of hydrocar- 

 bons is further enormously extended by the 

 possibility of double and treble unions be- 

 tween pairs of carbon atoms, as in ethylene, 



and acetylene, 



H-C^C-H 



Further, more than one double or treble 

 bond, or single, double, and treble bonds in 

 combination, may occur, as in the well-known 

 substances CH 3 - CH = CH 2 , CH 3 - C ■ CH, 

 CH 2 =C = CH 2 , etc. 



Finally, the carbon atoms possess the prop- 

 erty of uniting to form ring compounds in 

 great variety, e.g. 



H H 



CH 2 C C 



/\ s\ s\ 



CH 2 CH 2 HC CH 2 HC CH 



CH2 CH2 HC CH2 HC CH 



\/ v x/ 



CH 2 C C 



H H 



