116 ECOLOGICAL FOUNDATIONS OF ZOOGEOGRAPHY 



in warehouses, not a single species having spread so as to have come 

 into competition with native European forms. 55 



All these considerations support the theory that the forms now 

 inhabiting the southern hemisphere, with a limited or discontinuous 

 distribution, once inhabited the northern land masses, where they then 

 enj oyed the same continuity of distribution as the more modern north- 

 ern groups, which have driven their predecessors to the south. 34 



It has been suggested also that the Eurasian forms are similarly 

 superior to the North American, and this appears to be true to a 

 certain extent, witness the sparrow and starling, the house rats and 

 house mouse, the carp, and the host of insect pests introduced from 

 Europe. In the contrary direction, however, certain North American 

 animals have proved themselves almost equally able to spread in com- 

 petition with European forms, notably Phylloxera (the grape-root 

 louse), and the muskrat, so that the superiority of Eurasian forms 

 is certainly not without exception. In so far as such a superiority 

 exists, it may be due to the more stringent natural selection in the 

 larger field. 



The Reibisch-Simroth "pendulation theory" 56 requires brief men- 

 tion. It attempts to explain animal distribution on the basis of a 

 theoretically assumed cosmic process, the periodic change of the posi- 

 tion of the pole on the earth's surface in a meridian whose poles are 

 in Sumatra and Ecuador. These changes carry with them climatic 

 changes, most pronounced in the path of the pole, absent at the ends 

 of the imaginary axis, which induce and direct the migrations of the 

 faunae. A detailed consideration of this theory is unnecessary here, 

 for in spite of the support drawn by Simroth from his vast personal 

 knowledge of distribution, neither the premises for nor the conclusions 

 from this hypothesis will bear critical examination. 57 



Faunal regions. — The explanation of the principal features of the 

 present distribution of animals is to be found in the changes in faunal 

 barriers in the course of geologic time. The study of the actual data of 

 distribution can thus become fruitful only if it is based on the phylo- 

 genetic relations of the animals in the various regions and takes into 

 consideration the geologic and palaeontologic data. Faunal lists and 

 statistics, unless subjected to phylogenetic and geologic analysis, are 

 fruitless as a means of inquiry. Regions may thus be distinguished in 

 which the fauna, at least with respect to certain classes, is more or 

 less homogeneous. The earth was divided into such regions on the 

 basis of its bird faunae by Sclater; and Wallace, with principal con- 

 sideration of the mammals, has adopted a quite similar division. 

 Wallace believed that this division into "regions" would apply to all 



