116 MENTAL EVOLUTION IN ANIMALS. 



what I have marked off as the second and third stages of 

 conscious memory in the largest acceptation of the term — the 

 stages, that is, where, without any association of ideas, a pre- 

 sent sensation is perceived as like or unlike a past one. It 

 makes no essential difference whether the past sensation was 

 actually experienced by the individual itself, or bequeathed 

 to it, so to speak, by its ancestors. For it makes no essential 

 difference whether the nervous changes which constitute the 

 obverse aspect of the perceptive aptitude were occasioned 

 during the life-time of the individual, or during that of the 

 species and afterwards impressed by heredity on the indi- 

 vidual. In either case the psychological as well as the 

 physiological result is the same ; a present sensation is alike 

 perceived by the individual as like or unlike a past sensation. 

 It is not easy at first to grasp the truth of this statement ; 

 but the source of the difficulty is in not clearly distinguish- 

 ing between memory and the association of ideas. Memory 

 in its lower stages which we are now considering has, in my 

 opinion, nothing to do with the association of ideas. It only 

 has to do with perceiving a present sensation as like or unlike 

 a past sensation, which never can have formed the object of 

 an idea between times, and which does not even arise as an 

 ideal remembrance when the sensation again occurs. In 

 other words, there is no act of conscious comparison between 

 the two sensations ; there is not even any act of ideation ; 

 but the past sensation has left its record in the nervous tissues 

 of the animal in such wise that when it again occurs it 

 emerges into consciousness as a feeling that is familiar — or if 

 another unlike sensation takes its place, this emerges into 

 consciousness as a feeling that is not familiar. And whether 

 such feelings of familiarity or unfamiliarity arise in the 

 experience of the individual or in that of the species, makes, 

 as I have said, no essential difference either in the physiolo- 

 gical or in the psychological aspect of the case. 



As showing how close is the connection between here- 

 ditary memory, or instinct, and memory individually acquired, 

 I shall briefly state some very interesting experiments which 

 were made by Professor Preyer on newly-hatched chickens. 

 He laid before a newly-hatched chicken some cooked white 

 of egg, some cooked yolk of egg, and some millet seed. The 

 chick pecked at all three, but no more frequently at the two 

 latter than it did at pieces of egg-shell, grains of sand, or the 



