On the Diptera of the Amber-fauna. 321 
whether the existing intercourse between the two continents is 
sufficient to account for the large number of species common to 
both. Iam satisfied that it has to be answered negatively. 
In order to investigate the influence of a prolonged intercourse 
of this kind between two countries separated by a sea, I have 
repeatedly directed my attention to the comparison of the Dip- 
terous faunas in the countries surrounding the Mediterranean. 
These investigations, for which I possess abundant materials, 
. have made me, as far as it was possible, thoroughly acquainted 
with the influence exercised by an intercourse of this kind on 
the intermingling of the faunas, and have afforded me a measure 
of this influence. In drawing a conclusion from the extent of 
these influences in the countries adjacent to the Mediterranean, 
to the extent of the same influences as existing in consequence 
of the intercourse between Europe and America, we have to 
take into account the comparatively recent epoch when this lat- 
ter intercourse began, the much greater distance between the 
two continents, and before all, the much greater length of time 
required for a passage between them, especially in former years. 
In'view of all these causes, tending to diminish the probable 
influence of the intercourse on the intermingling of the faunas, 
We cannot possibly admit that the occurrence of such a large 
number of species, common to both sides of the ocean, should be 
merely the result of an intermingling brought about by this in- 
urse. It should be borne in mind that it is not with one 
from Europe to America; it can hardly be doubted that Scenopinus 
Senestralis and S. levifrons can easily be brought over in ships; 
the conformity of many species of Scatophaga and rborus can. 
easily found in their mode of life; nor will it appear very extra- 
Scribed as a European species, under the name of M. cimbu iformis ; 
that Hristalis on pe North America, should be a de- 
Scendant of European parents, is easily possible, as a ship affords 
the necessary conditions for the preservation of the larves. It 
Au. Jour. Sct.—Szcoxp Sentes, Vou. XXXVII, No. 111.—May, 1864, 
42 
