314 SENSATION AND THE SENSIFEEOUS ORGANS 



of one of these tunes, and the more feeble the 

 agent, the more delicate must be the mobility of 

 the stop. 1 



But, if this be true, if the recipient part of the 

 serisiferous apparatus is in all cases, merely a me- 

 chanism affected by coarser or finer kinds of 

 material motion, we might expect to find that all 

 sense organs are fundamentally alike, and result 

 from the modification of the same morphological 

 elements. And this is exactly what does result 

 from all recent histological and embryological in- 

 vestigations. 



It has been seen that the receptive part of the 

 olfactory apparatus is a slightly modified epi- 

 thelium, which lines an olfactory chamber deeply 

 seated between the orbits in adult human beings. 

 But, if we trace back the nasal chambers to their 

 origin in the embryo, we find, that, to begin with, 

 they are mere depressions of the skin of the forepart 

 of the head, lined by a continuation of the general 

 epidermis. These depressions become pits, and 

 the pits, by the growth of the adjacent parts, 

 gradually acquire the position which they finally 

 occupy. The olfactory organ, therefore, is a 

 specially modified part of the general integu- 

 ment. 



1 "Chaque fibre est une espece de touche oil de marteau 

 destine a rendre un certain ton. " Bonnet, Essai de Psychologic, 

 chap. iv. 



