FISHERY PROBLEMS 173 



the sea." The maximum temperature of waters frequented 

 by sardines is 68. "Above this temperature," says 

 M. Mader, " the sardines leave the surface and search 

 for better conditions in the submarine layers of the sea." 

 In the case of the herring, M. Canu has shown that the 

 range of temperature is 27 ; the minimum being 39*2 in 

 January and the maximum 66' 2 in November. In the case 

 of the tunny the range is 12-6. The mackerel and the 

 cod readily pass from cold to warm water. Moreover, 

 the fact that fifteen species are common to the North 

 Sea, the North and the South Atlantic, and the 

 Mediterranean is sufficient proof of the great tolerance 

 of fish as regards temperature 1 and of their tolerance as 

 regards salinity, 2 for the two factors are closely connected. 

 What is the cause of this tolerance ? Life itself. 



Thanks to assimilation, which transforms food into 

 muscles, blood, and bones, the living creature is in a 

 state of continual transformation ; it is a marvellously 

 complicated mechanism, which at all times is demolishing 

 and reconstructing itself; it is a piece of mechanism 

 in unstable equilibrium. According to the phrase of 

 M. Le Dantec, existence is a struggle and life is a victory. 

 Fish, in consequence, represent a continual triumph. 

 But, it may be asked, over what is their triumph ? Over 

 their environment ; over the medium that envelops 

 them. Although they are the lowest of the vertebrates, 

 they occupy a very high position in the zoological scale. 

 Placed in inclement surroundings, they resist them 

 instance the sardines in water at 50 but in the face of 

 danger, of certain death, or perhaps I should say before 

 the approach of certain defeat, they respond instance 

 the herring of the Kattegat somewhat as did the Russians 

 before Napoleon, proving to mankind that flight some- 

 1 See p. 30. a See p. 71. 



