X.] IN ANIMALS AND MAN. 59 



timid ; it needs to be extremely sensitive to every sound if it is 

 to continue to exist as a species. Hence we can perhaps to 

 some extent understand v^hy the rabbit has 7800 cells in its 

 auditory organ, although this implies the most astonishing 

 delicacy of ear. We must not hov^ever assume that each of 

 these cells is set to a different note, but rather that the four 

 cells of each transverse row are fitted to receive the same vibra- 

 tion. There remains, however, a surprisingly large number 

 of different note-sensations, i. e. nearly 2000. We can realize 

 how very delicate hearing must be, which can appreciate only 

 1000 different notes, when we remember that a concert grand 

 piano contains only 87 different notes. If we reckon that the 

 auditory organ can appreciate a somewhat longer scale, namely 

 that of a hundred notes situated at the distance of semitones, it 

 follows that the interval between two consecutive semitones 

 would contain nearly 19 intermediate sounds. The human 

 ear, when very highly trained, can distinguish nearly 30 inter- 

 mediate notes between A and B-flat, a rather larger number 

 than the difference between the numbers of their respective 

 vibrations in a second, — (A = 440, B-flat = 467.5). 



If then the mammalian auditory organ must attain so high 

 a pitch of perfection lest it should be inadequate in the struggle 

 for life, it is clear that the part of the brain by which notes are 

 perceived, the auditory centre, must possess a corresponding 

 degree of organization. We may indeed assume it to be 

 certain that a corresponding degree of development is found 

 in those layers of nerve-cells and nerve-fibres in the auditory 

 centre, the so-called ' field of memory,' which serve as the 

 material basis of the memory of auditory perceptions. Aristotle 

 was quite correct in maintaining that ' animals devoid of memor}'' 

 would be unable to perceive even the difference between two 

 successive notes \' But an elaborate auditory organ would be 

 of little or no value to such animals; they would be unable to 

 discriminate between the sound of an enemy and that of their 

 prey, for they could not compare the note they were hearing 

 with that previously heard, the latter having wholly faded from 

 their consciousness. 



It is much to be regretted that we can know with certainty 

 in but few cases how far an animal is capable of perceiving 



^ I quote from C. Stumpf, ' Tonpsychologie,' Bd. i, p. 279. 



