STEJ NEGER] ANIMALS AND PLANTS OF NORWAY 459 
incite further studies of the faunas and floras involved from the 
standpoint of this theory, in order that its merits or demerits may 
be thoroughly tested. The essay deals principally with biogeographic 
problems, but where it has been found necessary to introduce mor- 
phological matter in order to prove relationship, such questions are 
also discussed. Certain geological considerations which could not 
well be avoided have been set forth with due reserve, and in the most 
tentative manner. 
In the course of his investigations the biogeographer when study- 
ing the dispersal of certain biota and their immigration into other 
regions is frequently facing facts which compel him to assume that 
the animals and plants have crossed territory now covered by the 
sea. The first question he then asks himself is whether there is 
any geological evidence in support of his theory. If not a geologist 
himself, he begins to study the geological literature. It has been 
my experience that whatever view I have taken, or from whatever 
side I have been viewing a question of this nature, I have always 
been able to find a geological theory and a geologist quotable in 
defence of my contention. Do I need a land connection in a cer- 
tain place, there is always some geologist at hand willing to lift 
the ocean’s bed thousands of fathoms even in comparatively recent 
times. If the views I have advanced concerning the biotic dispersal 
do not commend themselves to my fellow student, he may with 
equal confidence search the geological literature and sustain his 
opinion with quotations diametrically opposed. It is comparatively 
seldom that we are able to find paleontological evidence, and even 
then we are not always safe. Under these circumstances it seems 
to be the wisest course for the biogeographer to abide by the results 
to which he is led by his study of the present geographical distribu- 
tion. If he can show then that his theories are not inconsistent 
with accepted principles and with the general outline of conservative 
geological opinion, he must remain satisfied. The details and the 
controversial points he may safely leave out, unless his own re- 
searches bear directly upon the latter. 
The immigration of the biota of the Skandinavian peninsula after 
the great glacial period had destroyed most of the higher life pre- 
viously existing there was comparatively early recognized by 
Swedish naturalists as having taken place along two different routes, 
viz., from the south across one or more Baltic land connections and 
a northeastern one over Finland and northwestern Russia. These 
two elements, the one descended from the biota of the central 
