444 THE BRAIN". 



felt at the time. We do not take food or drink because we know 

 that they are necessary to support life, much less because we under- 

 stand the mode in which they accomplish this object ; but merely 

 because we desire them whenever we feel the sensation of hunger 

 and thirst. 



All actions of this nature are termed instinctive. They are volun- 

 tary in character, but are performed blindly ; that is, without any 

 idea of the ultimate object to be accomplished by them, and simply 

 in consequence of the receipt of a 1 particular sensation. Accord- 

 ingly experience, judgment, and adaptation have nothing to do with 

 these actions. Thus the bee builds his cell on the plan of a mathe- 

 matical figure, without performing any mathematical calculation. 

 The silkworm wraps himself in a cocoon of his own spinning, 

 certainly without knowing that it is to afford him shelter during 

 the period of his metamorphosis. The fowl incubates her eggs 

 and keeps them at the proper temperature for development, simply 

 because the sight of them creates in her a desire to do so. The 

 habits of these animals, it is true, are so arranged by nature, that 

 such instinctive actions are always calculated to accomplish an 

 ultimate object. But this calculation is not made by the animal 

 himself, and does not form any part of his mental operations. 

 There is consequently no improvement in the mode of performing 

 such actions, and but little deviation under a variety of circum- 

 stances. 



The third kind of reflex action requires the co-operation of the 

 hemispheres. Here, the nervous impression is not only conveyed 

 to the tuber annulare and converted into a sensation, but, still 

 following upward the course of the fibres to the cerebrum, it there 

 gives rise to a special train of ideas. We understand then the 

 external source of the sensation, the manner in which it is calcu- 

 lated to affect us, and how by our actions we may turn it to our 

 advantage or otherwise. The action which follows, therefore, in 

 these cases, is not simply voluntary but reasonable. It does not 

 depend directly upon the external sensation, but upon an intellec- 

 tual process which intervenes between the sensation and the voli- 

 tion. These actions are distinguished, accordingly, by a character 

 of definite contrivance, and a conscious adaptation of means to 

 ends ; characteristics which do not belong to any other operations 

 of the nervous system. 



The possession of this kind of intelligence and reasoning power 

 is not confined to the human species. We have already seen that 



