386 



LAND ANIMALS 



as the cube of the linear dimensions and surface only as the square. 

 A more considerable body size therefore serves to reduce the heat 

 radiation. With this basic fact in view, it is significant that among 

 homoiothermal animals the same species attains a greater body size in 

 colder regions than in the warmer ones, and that in closely related 

 species the larger ones inhabit the colder climates. This is in direct 

 contrast with the reaction of the poikilothermal animals, such as 

 reptiles and amphibians, which are smaller in colder regions. This 

 principle has been called "Bergmann's Rule" after its discoverer 26 ; 

 it is a phenomenon of animal geography of great importance. 



A striking corroboration of the Bergmannian principle is offered 

 by the geographical distribution of the penguins, as the following table 

 shows : 



Species 

 A ptenodytes forsteri 



Body 

 Length in Weight in 

 Millimeters Kilograms 



1000-1200 



34.4 



Distribution 

 Antarctic continent, certainly 

 the farthest south of all its 

 relatives, exceptionally up 

 to 61° northward. 

 South to 55° (Macquarie Is- 

 lands). 

 South to 60° 30' (Paulet and 

 Dundee Islands), mostly 

 between 47° and 45°.° 

 South to 66°. Most northerly 

 breeding places South Ork- 

 ney Islands. 6 

 South to 64° 30' (Seymour 

 Islands), north to 52° south 

 latitude. 

 South to 61° (South Orkney 



Islands), north to 46° 30'. 

 South to 55° (Tierra del Fu- 

 ego), north to 37° (Tristan 

 da Cunha). 

 South to 52° (Falkland Is- 

 lands). 6 

 South to 34° 30' (Cape), north 



to 17° (Great Fish Bay). 

 South to 46° (New Zealand); 



southern Australia 38°. 

 Equatorial (Galapagos 

 Islands). 



<■ More stationary than P. adeliae, in the antarctic region even during the winter. 

 b Distinctly migratory; goes northward for breeding. 

 c Breed in caves. 



