PLANTS AND ANIMALS. 151 



them off. Those who do not put on armour 

 generally protect themselves by acrid, bitter and 

 poisonous secretions. No doubt they succeed to 

 a certain extent, but it always happens that some 

 of their foes still get the better of them. 



Finally, the geological formation of a district 

 has considerable influence on the distribution of 

 life. Apart from the obvious fact that a desert 

 must be almost devoid of life, there are differences 

 between hill and dale, sandstone and granite, and 

 clay and gravel, which result in corresponding 

 variations in the fauna and flora. In British 

 Guiana some have gone so far as to say that they 

 can tell when an auriferous district has been 

 reached by the prevalence of certain kinds of 

 birds and monkeys. This can be easily under- 

 stood when the close connection of the trees with 

 the soil, and the fruit with the animals, is con- 

 sidered. As in the case of civilised countries the 

 number of inhabitants depends a great deal on 

 the food supply, so here the denizens of the forest 

 vary from the same cause. 



