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 



