On the Diptera of the Amber-fauna. 315 
yaise this question and to proceed to the comparison with living 
species. Since the very beginning of my researches, that is, about 
seventeen years ago, I have very closely pursued this compari- 
son. I early found that some of the species enclosed in am 
h 
ose acquainted with the extreme difficulty attending, in 
many cases, the discovery of definite plastic characters for the 
discrimination of undoubtedly different species of living Diptera, 
will justify me if I attach less importance to the result of a single 
comparison of a fossil species, contained in amber, with an ex- 
tremely resembling living one, than to the general average of the 
results of such comparisons. And this is, as already noticed 
above, that with the increase in quantity as well as in quality of 
materials for comparison, the differences which could be traced 
poorer materials. Thus, not only do we not possess any sufficient 
proof of the identity of any one species, contained in amber, 
with a living one, but the results heretofore obtained render it 
extremely probable that a still greater increase of materials for 
Investigation will enable us to discover specific distinctions even 
living species so closely resembling them is a very peculiar one. 
close link of relationship to 
additions to the number of old 
species, but are so to say, the one he bi species, is in my 
nion irresisti snreindiced observer. nT 
i On irresistible to any vad atiche sal distribution of the ivi é 
eci closely enecies enclosed in amber, le 
Species so closely related to some species patent sige 
