ANIMAL LIFE IN THE DEEP SEAS. 707 



proximate the conditions for the development 

 of animal life, which existed in the shallower 

 seas of past geological ages? I think they 

 do, or at least I believe they approach it as 

 nearly as anything can in the present order of 

 things upon earth ; for the depths of the ocean 

 alone can place animals under a pressure cor- 

 responding to that caused by the heavy atmo- 

 sphere of earlier periods. But, of course, such 

 high pressure as animals meet in great depths 

 cannot be a favorable condition for the devel- 

 opment of life ; hence the predominance of 

 lower forms in the deep sea. The rapid dim- 

 inution of light with the increasing depth, 

 and the small amount of free oxygen in these 

 waters under greater and greater pressure* 

 not to speak of other limitations arising from 

 the greater uniformity of the conditions of 

 existence, the reduced amount and less vari- 

 ety of nutritive substances, etc., etc., are so 

 many causes acting in the same direction and 

 with similar results. For all these reasons, I 

 have always expected to find that the animals 

 living in great depths would prove to be of a 

 standing, in the scale of structural complica- 

 tions, inferior to those found in shoal waters 

 or near shore ; and the correlation elsewhere 

 pointed out between the standing of animals 



