CRANIAL NERVES AND SENSE-ORGANS 251 



intervals are reckoned in the octave, the trained musician's ear 

 can recognise seventy, so that on Helmholtz's theory six or 

 seven fibres represent the minimal interval of appreciation in 

 man. 



Judging from the similarity in structure in the ear of man 

 and all other mammals it may fairly be supposed that the pro- 

 cess of receiving and perceiving aural impressions does not 

 materially differ. Herbivora have not such acute hearing as 

 carnivora ; but whether this acuity depends on the delicate 

 distinguishing of tones, such as the human ear is capable of, 

 may well be questioned. 



In man individual variations in the acuteness or delicacy of 

 hearing are partly inherited, partly acquired by practice ; and 

 in this respect savage races cannot claim anything like a general 

 superiority over civilised man. Necessity and constant practice 

 will develop the faculties in the roving inhabitants of wide 

 plains and vast prairies ; elsewhere the primitive peoples do 

 not acquire the same keen ear. For instance, among the 

 Papuans Dr. Rivers found the hearing no more acute than in 

 Europeans. 



(d) Sense of Taste. 



The physiology of taste is still very little understood. It is 

 supposed that even the lowest animals, provided they possess 

 an oral aperture, have taste-perceptions which are probably 

 situated in the mouth. This conjecture is supported by obser- 

 vations upon the selection of food in insects and crustaceans, 

 and by the researches of Forel and Will upon ants and wasps 

 in which it was found that ants cannot invariably recognise 

 poisonous substances. The explanations given by these two 

 observers do not agree. For Will surmises that the hairs or 

 rods in the pits round the mouth must be perforated for the 

 taste to penetrate them, while Forel denies this, and takes the 

 view that the taste passes by osmosis through the thin chitinous 

 covering especially when nerves participate in their structure. 

 Wolffs cups (pits) with central hairs and a chitinous ring, and 

 a double ganglion swelling connected with a nerve-fibre are 

 particularly numerous in those creatures to which we have to 

 attribute the most pronounced sense of taste, namely ants, 



