VII THE LOST ANTARCTICA 2 1/ 



northern Niphargus and Gammarus, but grading almost completely 

 into the latter. Both Niphargus and Gavimarus are absolutely 

 unknown from the tropics, but whether, like Bosmina, they occur 

 in the Andes and temperate South America is not known ; it 

 seems, however, probable that they have reached Southern 

 Australia by way of South America rather than through the 

 tropics of Asia and Australia, where there is no range of 

 mountains to permit the migration of a group of animals 

 apparently dependent ou a temperate climate. The other 

 common fresh-water Amphipod in temperate Australia and New 

 Zealand is Chiltonia, whose nearest ally is Hyalella from Lake 

 Titicaca on the Andes, and temperate South America. 



The Anaspidacea and Phreatoicidae, which are so characteristic 

 of temperate Australia, and are generally of an Alpine habit, 

 have never been found in South America, but the Anaspidacea 

 are represented by numerous marine forms in the Permian and 

 Carboniferous strata of the northern hemisphere, so that it is 

 probable that this group reached the southern hemisphere from 

 the north through America. 



The distribution of the fresh-water Crustacea, therefore, in the 

 temperate southern hemisphere affords strong evidence in favour 

 of the view that the chief land-masses of this hemisphere, which 

 are at present separated by such vast stretches of deep ocean, 

 were at no very remote epoch connected in such a way as to 

 permit of an intermixture of the temperate fauna of New Zealand, 

 Australia, and South America. While this connexion existed, 

 a certain number of forms characteristic of the northern hemi- 

 sphere, which had worked through the tropics by means of the 

 Andes, were enabled to reach temperate Australia and New 

 Zealand. The existence of a coast-line connecting the various 

 isolated parts of the southern hemisphere would, of course, also 

 account for the community which exists between their littoral 

 marine fauna. It is impossible to enter here into the nature of 

 this land-connexion which is becoming more and more a necessary 

 hypothesis for the student of geographical distribution, whatever 

 group of animals he may choose, but it may be remarked that the 

 connexion was probably by means of rays of land passing up from 

 an Antarctic continent to join the southernmost projections of 

 Tierra del Fuego, Tasmania, and New Zealand. 



