Ig2 EXPEDITION ANTARCTIQUE BELGE 



gleichfbrmieen alten allgemeinen Fauna cler Erde, die sich verhaltnissmàssig wenig verândert 

 haben so dass zwischen der arktischen und antarktischen Fauna eine grôssere Aehnlichkeit 

 besteht, als zwischen irgend welchen anderen Faunengebieten. ».... « der Unterschied gegen- 

 tiber der neuen Anschauung besteht aber darin, dass man frtiher die Aehnlichkeiten als âusser- 

 liche, durch das Leben unter gleichen Bedingungen erworbene hinstellte, wàhrend es sich in der 

 der That uni innerlichste, verwandtschaftliche unter annâhernd gleich vcrblicbcnc Aehnlichkeiten 

 handelt ('). » 



2. J. Murray. — « In the shallower reaches of the océan the materials on the bottom are 

 assorted and distributed by currents in a way that produces a great variety of conditions. 

 In some places there are siliceous or calcareous sands, in other places dead shells and pebbles ; 

 on submarine banks, rocks and boulders prevail ; in dépressions, fine muds and clays. On each 

 of thèse bottoms there is usually a very différent assemblage of animais. So that, although the 

 trawl may not in shallow water bring up such a variety of organisms in any single locality 

 as from deeper water, still the total number of gênera and species inhabiting the whole area of 

 depths less than 5o fathoms is recognised as much greater than in deeper water. With increa- 

 sing depth, not only the nature of the deposits, but the other physical conditions, become more 

 and more uniform, till a depth is reached along the continental shores facing the great océans 

 immediately below which the conditions become nearly uniform in ail parts of the world, and 

 wherc the fauna likewise présents a great uniformity. This depth is usually not far above nor 

 far below the ioo-fathoms Une, and is marked out by what I hâve elsewhere designated as the 

 Mud-line ("). » 



» If there were once a nearly universal climate over the whole océan, we may suppose 

 that the same species of benthonic animais were nearly every where présent in the shallow-water 

 zones. When cooling at the pôles set in, those animais with pelagic larvas would be killed out 

 or be forced to migrate towards the warmer tropics. By being able to limit the reproductive 

 process to the summer season, some of thèse organisms with free-swimming larvae hâve been 

 able to live on in the temperate régions, but in the tropical and coral-reef régions we hâve the 

 remuants of a once universally distributed shallow-water fauna. With the disappearance of 

 this shallow-water fauna from the polar régions its place would be occupied by the organisms 

 from the deeper mud-line, very few of which possess pelagic larvae. In this way we may account 

 fur the identity or similarity between the polar marine faunas and floras, the great abundance 

 of individuals and the relatively few species in the polar areas when compared with the tropical 

 area, as well as the greater likcness of the shallow-water polar animais to deep-sea species. » (') 



III. objections DE principe. — 1. G. PfefFer. — Sans parler des divergences d'opinion en ce 

 qui concerne les Climats Polaires au cours des Ages Géologiques ( 4 ), la théorie de M. G. Pfeffer 

 ne peut se soutenir, car : 



« From the preceding portions of the présent considération and argument, it appears 



(i) G. l'i i i : i i . I >ie niedere Thierwelt, etc. p. 45,,. 

 i '.) |. Murray. Summary of Results, etc. Vol. II. p. 1433. 

 - J. Murray and A. F. Renard. Deep-Sea Deposits. ( Voyage "fil. M. S. Challenger. 1891. pp. [S8 et 252) 



(3) J. . Summary of Results, etc. Vol. II. p. 1459. 



(4) J. W. Gkegory. Somi Problems oi \rctic Geology. [Nature. 1897. Vol. LVI. p. 35 1). 



