2 4 8 



nean, at the same season, to spawn, following the line of the 

 European continent when it arrives, and on its return after 

 spawning, taking the coast of Africa and passing on through 

 the Straits of Gibraltar to the Atlantic. 



Now it will be easy to explain the diminution of this fish 

 since historic times, by the fact that of the great quantities 

 which enter the Mediterranean to spawn some are caught 

 by the fishermen after spawning, but the great majority 

 before fulfilling this function. How then can we conclude 

 that the cause of this diminution is not owing to the action 

 of man ? 



It is quite true that many centuries may elapse before 

 the complete extinction of a migratory species from the 

 vast expanse of the main ; perhaps before this exhaustion 

 takes place some of those abnormal conditions may occur 

 in the history of our planet which will disturb the essential 

 conditions of the history of those species, but even in this re- 

 mote contingency we must not lose sight of the fact that the 

 biological regions are not unlimited, and that every species 

 seeks out its abode where nature and its kindred elements 

 have produced the required conditions, some species being 

 only able to live in low temperature, others in high ones, 

 some again cannot live in estuaries, and those species which 

 are limited by temperature are again subdivided into others 

 separated by the pressure of the waters, some being obliged 

 to live at a great depth compared with others, and among 

 other limitations there is the question of food and shelter, 

 the appropriate motion of the currents ; and lastly, that the 

 depletion be not carried to such an extent as to prejudice 

 food-supply, and thus be the first step towards an end of the 

 industry. 



It is now time to enter on the second head of the theory 

 propounded. We have said that the depletion of the 



