6 BIOLOGICAL SOCIETY OF WASHINGTON. 



In general it seems as if we might safely assume that the com 

 position of abyssal sea water shows no very important differ 

 ences from that of other sea water and that the animals exist 

 ing in it are not exposed to any peculiar influences arising from 

 this source alone. 



This cannot be said of the physical conditions. Everyone 

 knows how oppressive to the bather is the weight of the sea 

 water at only a few feet below the surface, and how difficult it 

 is to dive, still more to remain on the bottom, if only for a few 

 seconds. 



But it is difficult to convey any adequate idea of the pressure 

 at such a depth as 2,000 fathoms, or about two miles below the 

 surface. 



Rope made impervious by tarring is said to have become 

 reduced one-third in its diameter by a descent into these depths. 

 Any hollow object not pervious or elastic, is at once crushed. 

 There is no doubt that at some points on the ocean floor the 

 pressure may amount to several tons to the square inch. 



If we recall that the average pressure in steam boilers is pro 

 bably much less than one hundred pounds to the square inch 

 it may help toward an appreciation of the abyssal conditions. 



The inevitable conclusion is, therefore, that all the animals 

 living under these conditions must have their tissues so consti 

 tuted as to permit the free permeation of the water through 

 every part in order that the pressure may be equalized. How 

 this is possible without putting an end to all organic functions 

 is perhaps the greatest mystery of abyssal life. How can a 

 large egg, like those of various deep-sea animals, pass through 

 the stages of segmentation and development, with every mole 

 cule of its structure in actual contact with ordinary sea water 

 and every solid particle subjected to a pressure of say a thou 

 sand pounds to the square inch ? 



