OF THE KERGUELEN REGION OF THE GREAT SOUTHERN OCEAN. o45 



the tropics ; if, in short, the marine faunas towards either pole are genetically more 

 closely related to each other than to any intervening fauna, then we are face to 

 face with one of the most remarkable facts in the distribution of organisms on the 

 surface of the globe. A study and comparison of Arctic and Antarctic marine faunas 

 and floras seem indeed to lead directly to very important suggestions as to the past 

 history of the earth and the gradual evolution to the physical and biological conditions 

 which now prevail over its surface. 



But apart altogether from the interesting questions here mooted, it is important at 

 the present time, when there is a prospect of a renewal of Antarctic exploration, to 

 summarise our knowledge of the marine fauna of the far south, and to point out the 

 interesting scientific results that would likely flow from a thorough exploration of these 

 regions with modern appliances. However, before proceeding to deal with the biological 

 observations of the Challenger Expedition during the cruise to the Antarctic Eegions, 

 it is desirable to recapitulate briefly the present state of our knowledge concerning the 

 geographical, bathymetrical, and physical conditions of the Great Southern Ocean. 



The Great Southern Ocean. 



Position and Extent. — The name Great Southern Ocean is usually given by geo- 

 graphers to that great belt of water surrounding the world in the Southern Hemisphere 

 between the parallels of 40° S. and the Antarctic Circle (66° 30' S.). The most important 

 land mass interrupting this continuous band of water is the southern end of South 

 America, which extends as far south as 56° S. The South Island of New Zealand, 

 Tasmania, Kerguelen, and numerous smaller oceanic islands, are also situated within 

 the limits of this great circumpolar ocean. 



The boundaries are wholly imaginary and artificial, and are not marked off by any 

 natural features on the surface of the planet ; still for convenience of description artificial 

 boundaries are most useful. The Great Southern Ocean is then broadly divided into 

 three regions, merging on their northern limits into the South Atlantic, the South Pacific, 

 and the Indian Ocean. On its southern limit the Great Southern Ocean merges into the 

 ice-bound Antarctic Ocean, situated to the south of the Antarctic Circle. 



The area of the Southern Ocean is estimated at about 26,158,850 square miles 

 (67,749,800 square kilometres), or about 18 per cent, of the total water-covered surface 

 of the earth. 



Depth. — On either side of the parallel of 40° S. we have a large number of trust- 

 worthy soundings extending right around the world, and an examination of these shows 

 that at its northern limit the Southern Ocean has an average depth of about 2300 fathoms 

 (4206 metres) or 1\ English miles. Southward of this line of soundings our knowledge 

 rf the depth of the Southern Ocean is very scanty. During her Antarctic trip the 

 hallenger obtained 11 soundings in depths exceeding 1000 fathoms (1829 metres), the 

 lepths ranging from 1260 to 2600 fathoms (2304 to 4755 metres). Five of these 



