THE TROUT JUMP. 31 



old Greek doctrine that man is the measure of all 

 things seems especially to beset us on every side. 

 Our own consciousness being the only consciousness 

 which we can experimentally examine, we are pecul- 

 iarly liable to accept its component elements as being 

 the component elements of all other consciousness 

 whatsoever. It is very hard some philosophers have 

 even told us it is impossible to construct a comparative 

 psychology, as we can construct a comparative osteology 

 of a comparative philology. All the other minds about 

 which we can obtain even the second-hand information 

 given us by language are still human minds ; and for the 

 animal consciousness generally we are reduced to very 

 inferential and doubtful data. 



Yet even here a good deal can be done by careful sift- 

 ing of facts, if only we know what facts to sift. The 

 general principle of nihil est in intellectu stands us in 

 good stead when once we have been able to discover 

 what was before in sensu and this we can often do 

 provided we take the trouble to follow out all the hints 

 supplied us by the nervous system and by the habits or 

 peculiarities of animals. In some fishes, for instance, 

 there is every indication of the preponderance of smell 

 over sight as an intellectual and guiding sense. In the 

 sharks and rays the membrane of the nose is enormously 

 developed ; the olfactory nerve is by far the largest and 

 most important in the body ; the central organs directly 

 or indirectly connected with it form the main mass of 

 the brain ; and the indications of habit, as well as the 

 sniffing-muscles attached to the nostrils, all go to show 

 that smell is really the chief sense-endowment of these 

 predatory species. On the other hand, their eyes are 

 relatively small and poorly developed, their optic nerves 

 and lobes are unimportant, and the general indications 



