J. W. Fewkes — Deep-Sea Medusae. 167 



modern growth. It is barely thirty years ago that naturalists 

 almost universally believed the abysses of the ocean to be 

 deserts as far as life is concerned. Deep-sea exploration has, 

 however, not only revealed the fact that the ocean bed at great 

 depths is peopled by a rich and varied fauna, but also that the 

 animals which constitute that fauna are peculiar and markedly 

 different from those found in shallow waters. 



It would seem a most extraordinary exception, if after the 

 floor of the ocean at great depths had been found to be in- 

 habited, the fathoms on fathoms of water through which the 

 sounding weight passes to reach those depths are destitute of 

 life. In mid-ocean, where there is a highly varied nomadic 

 life upon the surface and where the dredge has brought up 

 from the ocean bed a characteristic assemblage of animals, are 

 we to suppose that between these places there is not a repre- 

 sentative fauna, or must we conclude that after we sink a few 

 fathoms below the surface, life ceases, and that it is not until 

 we come to the floor of the ocean that life again appears ? If 

 between these two limits there is a fauna, is that fauna the 

 same as that found at the surface, or is it characteristic ? Can 

 the animals which compose it be circumscribed in bathy- 

 metrical zones out of which they cannot pass with impunity ? 

 Do we, in short, have in the nomadic oceanic life a change of 

 fauna as we sink below the surface ? 



Xaturalists have been led to suppose that since we find 

 peculiar modifications in animals living upon the sea bottom at 

 great depths, we should necessarily look for the same variation 

 among nomadic animals at intermediate depths. It would then 

 seem probable that there are bathy metrical zones for free- 

 swimming animals, and that these animals are characteristic as 

 compared with others which live at the surface. An investi- 

 gation of the character of this fauna, if such there be, has an 

 interest to the evolutionist, -for it might be supposed to 

 acquaint him with facts bearing on the general characters of 

 the ancestors of certain genera of surface life. 



I can imagine few places on the earth's surface where the 

 uniformity of physical conditions is greater than in the depths 

 of the sea. I do not mean, as might be supposed, necessarily 

 on the floor of the ocean, but at the depth of say one thousand 

 fathoms separated from the ocean bed by a wall of water of 

 the same depth. Here, if anywhere, we may look for uniform- 

 ity of conditions and if environment has anything to do with 

 modifications in the generic forms of animal life, here we can 

 expect to discover animals which preserve ancestral features. 

 On the surface of the ocean there are changes of temperature, 

 and of light, and climatic variations ; at the floor of the ocean 

 there may be reactions of the interior of the earth upon its 



