OF THE INTELLIGENCE AND OF INSTINCT. 163 



way ; but they continue also to labour (and this is why we 

 say "blind instinct") when their labours can be of no avail. 

 Such labours cannot be ascribed to any acts of intelligence, 

 but resemble rather those which lead the infant to the breast 

 of its parent. 



So varied are the instincts of animals, that we could only 

 venture in a brief manual such as this to speak of a few 

 these we shall select from amongst the more remarkable. 



320. The principal instinctive actions may be arranged 

 in three classes, according as they refer to the preservation of 

 the species, to that of the individual, or to its relations with 

 other animals. 



321. Of the instincts bestowed on animals by nature, 

 none is more remarkable than that inciting them to live ex- 

 clusively on certain substances. Some of the simplest ani- 

 mals are without instinct, and swallow whatever comes near 

 them : such is the case with various zoophytes ; but it is 

 quite otherwise with most, which refuse obstinately all sorts 

 of food but one. Some live exclusively on animal food, others 

 on vegetable ; others only on certain plants, or the leaves and 

 fruit of but one plant, showing an indifference for all others ; 



Fig. 115. Ant-lion. 



and what is most remarkable is, that at a certain stage of 

 their growth they will abandon this kind of food for another, 

 with the use of which they were previously wholly unac- 

 quainted. Thus certain insects carnivorous in the larva 

 state, become phytivorous when perfect : and frogs, which 

 when tadpoles are vegetarians, become carnivorous as frogs. 



322. With the instinct, nature of course gives the ability 

 to gratify it. 



M 2 



