31 6 MENTAL EVOLUTION IN ANIMALS. 



has no reference to any question of instinct — for, unlike the 

 case of insects, the habit is much too exceptional to be 

 regarded as instinctive— but to determining whether the 

 facts are clue to intelligent purpose or to some purely physio- 

 logical effects of fear. In the more remarkable of the above- 

 quoted cases, no doubt, the latter hypothesis is not available; 

 but it may be so in some of the others, and even where this 

 hypothesis is not available, it becomes most desirable to 

 understand the class of ideas which induce the animal to 

 behave in a manner so closely simulating death. Here, how- 

 ever, I am only concerned with showing that the difficulty of 

 arriving at such an understanding has nothing to do with the 

 present theory as to the formation of instinct. 



Feigning Injury. 



In the " Contemporary Review " (July 1875) the Duke 

 of Argyll, in an article on " Animal Instinct," argues that the 

 female duck could hardly have consciously learnt to imitate 

 the movements of a wounded bird ; and that the young merg- 

 ansers, which squat on the mud when alarmed and are thus 

 made inconspicuous while the old ones fly away, are in the 

 same case. Mr. Darwin, in some MS notes on this article, 

 observes that he agrees with the Duke in not ascribing the 

 deceptive movements of the female duck, &c, to conscious 

 imitation of wounded birds ; but thinks that a female bird 

 which, from solicitude for her nestlings, would endeavour to 

 fight a threatening quadruped as a hen does a dog, might, 

 by alternately attacking and retreating, inadvertently draw 

 the enemy away from the nest. Natural selection, acting on 

 this primitive habit, might then develop the running away 

 from the nest as an instinct ; and if, as is probable, carni- 

 vorous quadrupeds would be more likely to follow birds 

 apparently unable to fly than birds apparently well, the 

 action of drooping the wing, &c, might have been slowly 

 developed. 



The instinct of squatting shown by young birds, which 

 are thus rendered inconspicuous, was no doubt acquired in 

 the same way and for the same reason as the instinct of 

 shamming dead in insects. The instinct, however, in the 

 case of young birds may have originally been acquired by 

 older animals (due in the first instance to being partly 



