28 THE EVOLUTIONIST AT LARGE. 



which he gave to the monkeys at the 

 Zoo ; and one monkey after another opened 

 the bag, looked in upon the deadly foe of the 

 quadrumanous kind, and promptly dropped 

 the whole package with every gesture of 

 horror and dismay. Even man himself 

 though his instincts have all weakened so 

 greatly with the growth of his more plastic 

 intelligence, adapted to a wider and more 

 modifiable set of external circumstances 

 seems to retain a vague and original terror of 

 the serpentine form. 



If we think of parallel cases, it is not 

 curious that animals should thus instinctively 

 recognise their natural enemies. We are not 

 surprised that they recognise their own 

 fellows : and yet they must do so by means 

 of some equally strange automatic and in- 

 herited mechanism in their nervous system. 

 One butterfly can tell its mates at once from 

 a thousand other species, though it may differ 

 from some of them only by a single spot or 

 line, which would escape the notice of all but 



