284 ANIMAL FORCES. [ii. 



asleep on tlie way, are conscious of nothing, observe nothing 

 that they meet, and yet reach their destination. If it be 

 advanced, that these movements depend on obscure sensations, 

 (which, however, is not the case,) there are innumerable illus- 

 trations in lower animals, that are unanswerable. A frog uses 

 its legs quite differently, when it swims than when it leaps. 

 If, when decapitated, it be pinched, it leaps away, not because 

 an external sensation excites an instinct, but simply in virtue 

 of the nerve-action of an external impression. If, in leaping, 

 it falls into the water, it then uses its legs to swim, not because 

 the external sensation of the water excites the instinct to swim, 

 but because the external impression from the contact of the 

 water excites the movement as a nerve-action. This being 

 undoubted, why should it be presupposed that a living frog 

 leaps or swims only in consequence of the excitement of the 

 instinct by external sensations ? It is clear that it may do 

 both without external sensations, and without the development 

 of the instinct. Thus, it is manifest, that the movements are 

 probably often nerve-actions only, which we constantly suppose 

 to be sentient actions, because they are such in ourselves and 

 in other animals. 



557. We can manifestly see from these considerations, what 

 truth there is in the inference made from the performance of 

 volitional motions of animals, especially of those which are 

 instinctive, as to the existence of mind, and of sensations, and 

 volitional conceptions. If the most voluntary instinctive ac- 

 tions of animals really sentient and endowed with true instincts 

 can be excited by means of mere external impressions, and can 

 go on after their organism has been subjected to so great an 

 injury as decapitation, — or if volitional movements can be 

 excited and regulated under such circumstances, by various 

 and successive external impressions, just as if they were felt, 

 and so excite new instincts into operation (555, 556), it were 

 altogether unreasonable to infer from the apparently voluntary 

 movements of many animals, whose whole conceptive force is 

 of doubtful existence, that those movements in them are sen- 

 tient actions of true instincts, and the results of external sen- 

 sations; or to accept these as the sole decisive proof, that 

 they possess conceptions. When we consider how carefully 

 nature has provided, that in the apparent instincts of animals. 



