1 76 Instinct. 



positing them in their proper places, caring for them 

 as all other Salmon have done before ; although not 

 one of them ever saw the work done, as must be 

 the case when a stream is stocked, for the first time, 

 by eggs carried there from some other place. But 

 in general, we can trace the direct relation between 

 the instinctive act and the impression made upon 

 some sense. In all cases, where the acts depend 

 upon the impressions made upon the senses, the 

 act is performed when the impression is made ; and 

 in accordance with the impression, although the 

 impression maybe made in such away as to entire- 

 ly deceive the animal. There is in most animals, 

 certainly in some of them, very great power of dis- 

 cerning through the senses those characteristics 

 that are desirable or undesirable in an object ; 

 but when you imitate, in any way, those character- 

 istics, they act. Hence arise many cases of appar- 

 ent reasoning, that are nothing more than the vari- 

 ation of the action of Instinct to secure a given re- 

 lation of the animal to the world around him. 



Flies lay eggs upon the Carrion-plant,* because 

 its odor has the same relation to their sense of smell, 

 as the odor of putid flesh, upon which theiryoung can 

 feed ; but they make a mistake, because their young 

 cannot live upon the flower. Very young birds, 

 when any sound is made upon the edge of the nest, 

 open their bills, — as readily to the boy that comes 

 to rob the nest, as to the mother that comes to feed 

 them . The instinctive act, essential to life, is li7tked to 

 the sensation of sound. The hen is cheated by the 

 * Kirby. Bridg. Treat. 



