I 4 8 EVOLUTION AND NATURAL THEOLOGY. 



at least, owe their extermination either directly 

 or indirectly to human agency. 



Although the crocodiles and great serpents * 

 still survive the far-distant period when the 

 dominant forms of life were Eeptilian, the 

 crocodiles (and, indeed, some of the most for- 

 midable serpents, such as the Anaconda) belong 

 as much to the water as to the land; and aquatic 

 organisms are all developed on a much lower 

 plane than terrestrial, as we may perceive when 

 we reflect that nearly all the higher groups, 

 both of animals and plants, are terrestrial, or 

 at least amphibious ; while many of the lower 

 groups are exclusively aquatic. The iguanodon, 

 and other gigantic land reptiles gave place to 

 the more highly organised Mammalia two geo- 

 logical ages since. Herbert Spencer f says that 

 the crocodile and pike have no definite period 

 of growth, but continue to increase in size as 

 long as they live. He attributes this to their 

 sluggish habits, and to the comparatively small 

 exertion and expenditure of vital energy re- 



* There is some reason to suppose that serpents, and possibly some 

 forms of four-footed reptiles much larger and more formidable than 

 any now existing, may have survived till comparatively recent historic 

 ages. 



t "Biology," vol. i, p. 125, 126. 



