SIXTH DAY.] SENSES OF FISH. 157 



And this could hardly happen unless they confined 

 their migrations to a certain space in the sea, the 

 boundaries of which may be regarded as the shore 

 and the deep water, which may be considered as 

 effectual a limit almost as land; for fish do not 

 willingly haunt very deep water, that being even in 

 summer of low temperature, approaching to 40, 

 and containing little or no vegetable food or insects, 

 which the smaller fishes search for, and the larger 

 fishes follow the smaller. It is however possible, that 

 in winter, all fish fond of heat will seek water rather 

 deeper than in summer ; and charr and umbla in lakes 

 are usually found in the deepest parts, being fond of 

 cool water, and they come to spawn whenever the 

 shallow water of the lakes becomes cool, in October 

 or November. We cannot judge of the senses of 

 animals that breathe water, that separate air from 

 water by their gills ; but it seems probable, that, as 

 the quality of the water is connected with their life 

 and health, they must be exquisitely sensible to 

 changes in water, and must have similar relations to 

 it that an animal with the most delicate nasal 

 organs has to air. A vulture or a dog scents not 



average weight is fully fourteen pounds. 1 ' He adds, that it is rare 

 indeed for a fish returning through the common estuary, to miss its 

 way to its own river, even when first returning as a grilse, a fact in 

 favour of the explanation given by the author of the occurrence. J.D.] 



