310 MIND IN EVOLUTION CHAP. 



of corn, his whole energies being employed in watching." 

 Mr. St. John says : " When the sentry thinks that he has 

 performed a fair share of duty, he gives the nearest 

 bird to him a sharp peck. I have seen him some- 

 times pull out a bunch of feathers if the first hint is not 

 immediately attended to, and at the same time uttering 

 a querulous kind of cry." Mr. St. John was constantly 

 baulked by sentinel geese, and found that whole flocks of 

 swans would have their heads in the water except one 

 "who was relieved from time to time." Sentinels have 

 an alarm note. <c Ibex, marmots, and mountain-sheep 

 whistle, prairie dogs bark, elephants trumpet, wild geese 

 and swans have a kind of bugle call, rabbits stamp on 

 the ground, sheep do the same, and wild ducks, as the 

 writer has noticed, utter a very low caution quack to 

 signal c The enemy in sight.' ' 



The response to the alarm cry is no doubt an ordinary 

 case of an instinctive method of reaction perfected by ex- 

 perience, but the position and behaviour of the sentinel, 

 and in particular, the change of sentinels, are difficult to 

 explain without crediting the birds or beasts concerned with 

 some power of understanding one another and the purpose 

 they are fulfilling. Moreover, according to Brehm, 1 at 

 least one case has been observed in which the sentinels were 

 set as the direct result of experience. A marabout having 

 been shot in visiting a slaughter house, the survivors there- 

 after instituted a guard. There is surely a marked contrast 

 between such a use of experience and the mere pruning of 

 impulsive tendencies by pleasure and pain. In the latter 

 case a reaction is checked or encouraged by what an animal 

 has itself felt. In the former, a special contrivance is 

 adopted to avoid a fate which it has witnessed in the case 

 of another. 



2. The appearance of sympathy and attachment between 

 the higher animals may doubtless, in many cases, be ex- 

 plicable as the effect of hereditary methods of response to 

 stimulus as perfected by experience. Just as the smell may 

 direct the young to the udder, so the sight of the calf may 

 stimulate the cow to go towards it, or run after the cart 

 1 . Quoted by Schneider, p. 352 ; Brehm, VI, p. 522. 



