146 SALMONIA. 



same rivers to breed in which they were 

 born, or where they have spawned before. 

 And this could hardly happen unless they 

 limited their migrations to a certain space in 

 the sea, the boundaries of which may be 

 regarded as the shore and probably deep 

 water, which may be considered as effectual 

 a boundary almost as land ; for fish do not 

 willingly haunt very deep water, which even 

 in summer is of low temperature, approaching 

 to 40°, and which contains little or no veget- 

 able food or insects, which the smaller fishes 

 search for, and the larger fishes follow the 

 smaller. It is however possible, that in win- 

 ter, all fish fond of heat will seek water 

 rather deeper than in summer; and char 

 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 which breathe water, — 

 which separate air from water by their gills ; 

 but it seems probable that as the quality of 

 the water is connected with their life and 



