4 BIOLOGICAL SOCIETY OF WASHINGTON. 



are often very favorable for marine life. Currents of compara- 

 tively warm water, like the Gulf Stream, sweep along bring- 

 ing fresh pure water and supplies of food to the animals along 

 their track. The division between the abysses and the slopes 

 is rather a matter of temperature than of mere depth. But 

 the temperature itself is somewhat dependent on the depth, 

 the influence of the great warm currents rarely extending 

 below seven or eight hundred fathoms and this depth corre- 

 sponds roughly to a temperature of about forty degrees Fah- 

 renheit. Below this it diminishes as the depth increases, at 

 the rate of about one-tenth of a degree to one hundred fathoms 

 until the freezing point is reached, though there is no reason 

 to suppose that the abyssal water ever actually becomes con- 

 gealed. 



To this cold dark area of the Ocean bottom has been applied 

 the name of the Benthal or Abyssal region. 



To the region, chiefly on the continental slopes, between the 

 Litoral and Abyssal regions, I gave some years ago the name 

 of the Archibenthal Region. 



These divisions have been recognized by various writers and 

 have had several terms applied to them. Those I have men- 

 tioned seem to me as characteristic as any, and in some respects 

 more convenient than any I have heard used. 



Let us now consider the conditions under which life exists 

 in the Abyssal and Archibenthal regions. It may be premised 

 that the differences between them are largely of degree and 

 not of kind and do not require that the tw T o regions should be 

 considered separately. 



The chief characteristics reside in the composition of the sea 

 water, including its contained gases ; in the dynamic status of 

 the deeps, especially in relation to temperature and pressure ; 



