150 INTRODUCTION TO SCIENCE 



of our rivers in the wonderful eel-fare which 

 is one of the sights of Spring. If it is not fortunate, 

 it may take much more than a year to reach the 

 feeding-ground those that ascend the rivers of 

 the eastern Baltic have journeyed over three 

 thousand miles. Eventually, however, a large 

 number do pass up the streams, and there is a 

 long period of feeding and growing in the slow- 

 flowing reaches and in fish-stocked ponds. There 

 is never any breeding in fresh water, but after 

 some years restlessness seizes the adults as it 

 seized the larvae a restlessness due to a repro- 

 ductive, not a nutritive motive. There is an 

 excited return journey to the sea and they don 

 wedding garments of silver as they go, and be- 

 come large of eye. They appear to migrate 

 hundreds of miles, often out into the Atlantic to 

 the verge of the Deep Sea, where, as far as we 

 know, the individual life ends in giving rise to 

 new lives. In no case is there any return. 



We ask then what the Machine theory of Life 

 can make of a story like this, and it is only a type 

 of many. Let us keep to the second last chapter, 

 the migration to the spawning-grounds. Like 

 many other fishes, the eel requires specific condi- 

 tions of depth, salinity, and temperature. The 

 North Sea will not serve, for it is too shallow; 

 the Norwegian will not serve, for it is too cold. 



What can the physiology that is only applied 



