1902.] AND ANCIENT GEOGRAPHY. 269 



proper foundation has now been recognized and the opposite opinion 

 begins to prevail, that abnormal conditions of distribution are due 

 to just such changes of the physical conditions during a geological 

 past, and that cases of this kind may often enable us to draw con- 

 clusions as to the reconstruction of the old conditions. We may 

 safely assume that the character of the physical conditions of the 

 earth's surface has changed continuously and variously in the past 

 and that we possess among living animals many forms which express 

 in their present distribution not only the Tertiary state, but which 

 may also represent Mesozoic or even Palaeozoic conditions. Thus 

 it is evident that investigation of the present distribution cannot be 

 used as the starting point for the construction of any scheme. This 

 has been done, however, not only by Wallace — who entirely disre- 

 garded the above fact — but also by others, who paid due attention 

 to it. Indeed Osborn l has pronounced it the purpose of Zoogeog- 

 raphy to unite past and present distribution into one scheme, and 

 the same idea has led Jacobi 2 to attempt practically this union. 



But if we study the most prominent differences between past and 

 present we see that they are chiefly found in the different distribu- 

 tion of land and water, and that frequently in past times land con- 

 nections existed between parts which are now separated, or vice 

 versa; and thus it is self-evident that the solution of Osborn's 

 problem is simply impossible, since there is no way to express 

 separation and connection of the identical parts in one and the 

 same scheme. 3 



We consequently arrive at the following three conclusions : 



i. Any division of the earth's surface into zoogeographical regions 



which starts exclusively from the present distribution of animals, 



without considering its origin, must be unsatisfactory, since always 



, only certain cases can be taken in while others remain outside of this 



scheme. 



2. Considering the geological development of the distribution of 



1 H. F. Osborn, " The Geological and Faunal Relation of Europe and America 

 During the Tertiary Period, etc.," in Ann. N. Y. Acad. Sci., Vol. xiii, 1900, p. 

 48, and in Science, April 13, 1900, p. 563. 



"■* A. Jacobi, " Lage und Form biogeographischer Gebiete " fZeitsc/ir. Ges. 

 fuer Erdkunde, Berlin, Vol. xxxv, 1 900). 



3 This, of course, does not dispose entirely of Osborn's problem. On the con. 

 trary, it remains "the" problem of Zoogeography, only we have to change its 

 formal expression and to say that the historical union of past and present dislri» 

 bution is the purpose of zoogeographical study. 



