ZONES OF MARINE LIFE. 



499 



occupying the lower regions have experimen- 

 tally exhibited a greater tolerance of pressure 

 than those of the more superficial zones. 



But the distribution of marine life is also 

 influenced by the laws of oceanic temperature, 

 and by the depth. The most systematic obser- 

 vations upon this subject are the researches of 

 Professor E. Forbes in the ./Egean Sea, to which 

 allusion has already been made. As the result 

 of long-continued and carefully-conducted expe- 

 riments in that sea, it has been found that eight 

 regions or zones of depth may be distinguished, 

 each characterized by its peculiar inhabitants. 

 These regions are exhibited in the accom- 

 panying diagram. But there is a gradual 



transition observed in the character of the 

 inhabitants of these regions at their commence- 

 ment, and at their termination. A few from 

 below appear just before the termination of one 

 zone and the commencement of another. While, 

 however, this is the case, the lines of separation 

 are remarkably well defined, very few creatures 

 of the same species being found in more than 



