VARIATION OF INSTINCT IN DEFINITE LINES. 227 



laboriously given ; * and the only use it can be is that of 

 developing the powers of flight more rapidly than they 

 would develop if not thus assisted. 



Similarly, the singing of birds is certainly instinctive ; 

 yet it is improved by imitation and practice — the young 

 birds listening to the old and profiting by their instruction, 

 as is proved by the cases previously cited of birds which had 

 never heard the songs of their own species yet singing their 

 songs, but doing so " tentatively and imperfectly." 



Again, although terriers take to hunting rabbits instinc- 

 tively, it is usual, as I have myself observed, for their 

 parents to teach them, or lead on their natural instincts by 

 imitation, whereby the hereditary aptitude develops more 

 quickly than it would if left to itself. 



The Duke of Argyllf give a curious case, which he "knows 

 to be authentic," of a golden eagle in the possession of Mr. 

 W. Pike, Glendarry, Co. Mayo, which in the spring of 1877 

 laid three eggs. These Mr. Pike took away, and substituted 

 for them two goose eggs. The eagle hatched out the two 

 eggs. One of the goslings died, and was torn up by the 

 eagle to feed the survivor, " who, to the great tribulation of 

 its foster-parent, refused to touch it. . . .' The eagle, 

 however, in the course of time, taught the goose to eat flesh, 

 and (the goose having free exit and ingress to the eagle's 

 cage) always called it by a sharp bark whenever flesh is 

 given to it, when the goose hastens to the cage, and greedily 

 swallows all the flesh, &c, which the eagle gives it." 



Again, there is evidence to show that the knowledge 

 which animals display of poisonous herbs is of the nature of 

 a mixed instinct, due, to intelligent observation, imitation, 

 Datura! selection, and transmission; for, as Mr. Darwin points 

 out in the Appendix, " lambs turned out without their 

 mothers are very liable to eat poisonous herbs; and it seems 

 to lie certain that cattle, when first introduced into a country, 

 are killed by eating poisonous herbs, which the cattle already 

 introduced have learnt to avoid."} 



In tins case there is indeed no evidence of the young 



• Bur II. I);ivy gives an rvrount of iuoh laborious instruction m witnessed 

 by himself in Mi.- case of tin- golden eagle. Bee Animal Intelligence^ p. 290. 



t Nature, vol. xix, p. ."*.', i 



I Y'limtl on Shrrjt, p. 101; find Ann*, and \l<tj. Hut. SUt., 2nd ser., 

 v « ■ 1 n, p. 3GI, io. 



