576 A NATURALIST ON THE "CHALLENGER. 



he constantly obtained large catches of Pelagic animals, when 

 very few were obtainable at the surface. 



Pelagic animals are most widely- spread, closely similar forms 

 occurring in widely distant oceans. In this particular, the 

 Pelagic fauna resembles that of the deep sea. In the case of 

 the sea surface winds and currents are present both to aid or 

 limit the range of species, and the variety of climate acts 

 as a barrier. In the deep sea all these forms of restriction are, 

 however, absent. 



The Deep sea and its Fauna. — I have above briefly described 

 the vegetation and fauna of the ocean surface, because, did these 

 not exist, life would be impossible, or only extremely scanty, in 

 the deep-sea bottom. Before referring to the fauna of the deep 

 sea, it will be well to consider briefly the conditions under which 



it exists. 



If a globe, 40 feet in diameter, be taken to represent the 

 earth, this will be on the scale of 1 foot to 200 miles, or 1 inch 

 to 16f miles, or 88,000 feet.* Thus on such a globe the 

 highest mountain and the deepest sea would be on true propor- 

 tional scale represented severally by an elevation or depression 

 of } rd of an inch. Were the land surfaces and sea beds sculp- 

 tured in due proportion on the face of this globe, the surface 

 would at a little distance hardly appear roughened, so insig- 

 nificant is the altitude of the highest mountains and the depth 

 of even the deepest seas in proportion with the dimensions of 

 the earth itself. The oceans in relation to their superficial area 

 are as shallow as a sheet of water one hundred yards in diameter, 

 and only an inch in depth, t 



We are apt to form an erroneous impression as to the actual 

 shapes and distributions of the elevations and depressions on the 

 earth's surface, because only the very tops of the elevations stand 

 above water. The outlines of the various continents and islands 

 with which we are familiar on maps, are merely lines 

 marking the height to which the water reaches up. A very 



* Lieut. Gen. E. Strachey, E.E., F.R.S., "Lecture on Scientific 

 Geography." Proc. Geogr. Soc, 1877, p. 191. 



t James Croll, " Climate and Time," p. 135. • London, Daldy & Co., 

 1875. 



