30 BRITISH FRESH-WATER FISHES 



herrings, carps, and other families, there exists a more or less 

 elaborate connection between the air-bladder and the auditory- 

 process. 



In the lampreys the labyrinth consists only of two semi- 

 circular canals and a vestibule. 



Of the extent to which fishes exercise and are guided by the 

 sense of smell very little is known. Early writers upon angling 

 The sense prescribe various odoriferous unguents, calculated 

 of smell. ^-Q attract fishes to the bait ; but as the use of such 

 anointing has been entirely discontinued in modern practice, 

 these prescriptions must be regarded as purely empirical. Had 

 assafoetida, oil of ivy, or the other strong-smelling substances 

 recommended proved efficacious, fishermen would have been 

 slow to abandon them. It is said that trout are drawn from 

 long distances by the odour of potted salmon-roe ; but of this 

 I cannot testify from observation, the use, sale, or possession 

 of that article being contrary to law. Nevertheless, seeing that 

 all fishes, even the brainless lancelet, possess olfactory organs, 

 it is certain that they possess also the power of smelling. But 

 the exercise of this faculty differs from that of terrestrial 

 vertebrates in being totally disconnected with the machinery 

 and function of respiration. The " breath of his nostrils " 

 is the life of man ; his olfactory nerves vibrate to the odori- 

 ferous atoms borne on the atmosphere ; he cannot smell 

 without performing half the complete act of respiration — that 

 of inhaling ; and he cannot inhale properly, i.e.^ through the 

 nostrils, without being sensible of any odour strong enough to 

 excite his olfactory nerve. But fish breathe through the mouth 

 and gills, with which the nostril has no connection whatever ; * 

 the act, therefore, of admitting water to the nasal sac, whether 

 it be voluntary or unconscious, is quite independent of 

 breathing. 



In British fresh-water fish, with the exception of one 



* Except in the Dipnoi, such as lepidosiren and Protopterus, which 

 spend part of the year torpid in the dried mud of rivers. 



