ii] RHYTHMICAL CHANGE IN THE SEA 51 



the seasonal changes in the sea, for heredity has 

 stamped certain habits on its organisation, and even 

 if the conditions were to remain the same there 

 would still be periodicity in the life-processes. This 

 periodicity would ultimately be obliterated if the 

 conditions of life were always to remain strictly 

 uniform, but for a time it would manifest itself. If we 

 keep such a fish as an eel in an aquarium we shall find 

 that as the period of its life comes when it should 

 be migrating down to the sea in order to spawn in 

 the deep water off shore, various changes will occur 

 in spite of the fact that the animal is being kept in 

 water of uniform condition. When it reaches a 

 certain age it ought to be seeking water of great 

 depth, and if it is unable to do this its metabolism 

 becomes disturbed, since it is adjusting itself uncon- 

 sciously to inhabit water where the pressure is very 

 great, but it still is compelled to remain in the shallow 

 water of an aquarium tank. We find therefore that 

 bubbles of gas begin to form underneath the skin 

 because the pressure of the water is far less than 

 that to which the fish is adjusting itself by sheer 

 force of inheritance. 



We must regard heredity as a kind of flywheel 

 which causes an organism to undergo periodic changes : 

 reproductive changes, migrations, growth, etc. Apart 

 altogether from external stimuli the flywheel would 

 still revolve and the organisms would still display 



42 



