An Unknown Sense 345 



I have given it to young nostrils to sniff, nostrils 

 much more sensitive than mine : not one of us 

 has perceived the faintest trace of smell in the 

 caterpillar. When the Dog, famed for his scent, 

 becomes aware of the truffle underground, he 

 is guided by the tuber's savour, which is highly 

 appreciable by ourselves, even through the 

 thickness of the soil. I admit that the Dog has 

 a more subtle sense of smell than we have : it 

 is exercised at greater distances, it receives 

 more vivid and lasting impressions ; neverthe- 

 less, it is impressed by odorous effluvia which 

 becomes perceptible to our own nostrils under 

 the proper conditions of proximity. 



I will allow the Ammophila, if you like, a 

 scent as delicate as that of the Dog, more deli- 

 cate even ; but still a smell is needed ; and I 

 ask myself how that which is inodorous at the 

 very entrance to our nostrils can be odoriferous 

 to an insect through the intervening obstacle 

 of the ground. The senses, if they have the 

 same functions, have the same excitants, from 

 man to the Infusoria. No animal, so far as I 

 know, can see clearly in what to us is absolute 

 darkness. True, it may be said that, in the 

 zoological progression, perception, always funda- 

 mentally the same, has varying degrees of power : 

 this species is capable of more and that species 

 of less ; what is perceptible to one is impercept- 



