184 ZOOLOGICAL OEOGEAPHT 03? THE MALAX ARCHIPELAGO. 
of these countries must necessarily depend on the same physical 
changes which the Southern hemisphere has undergone ; and we 
are therefore led to conclude that insects are much less persistent 
in their specific forms than flowering plants, while among Mam- 
malia and land birds (in which no genus even is common to the 
countries in question) ^species must die and be replaced much more 
rapidly than in either. And this is exactly in accordance with the 
fact (well established by geology) that at a time when the shells 
of the European seas were almost all identical with species now 
living, the European Mammalia were almost all different. The 
duration of life of species would seem to be in an inverse propor- 
tion to their complexity of organization and vital activity. 
In the brief sketch I have now given of this interesting subject, 
such obvious and striking facts alone have been adduced as a tra- 
veller’s note-book can supply. The argument must therefore lose 
much of its weight from the absence of detail and accumulated 
examples. There is, however, such a very general accordance in 
the phenomena of distribution as separately deduced from the 
various classes or kingdoms of the organic world, that whenever 
one class of animals or plants exhibits in a clearly marked manner 
certain relations between two countries, the other classes will cer- 
tainly show similar ones, though it may be in a greater or a less 
degree. Birds and insects will teach us the same truths ; and even 
animals and plants, 'though existing under such different conditions, 
and multiplied and dispersed by such a generally distinct pro- 
cess, will never give conflicting testimony, however much they 
may differ as regards the amount of relationship between distant 
regions indicated by them, and consequently notwithstanding the 
greater or less weight either may have in the determining of 
questions of this nature. 
This is my apology for offering to the Linnean Society the pre- 
sent imperfect outline in anticipation of the more detailed proofs 
and illustrations which I hope to bring forward on a future 
occasion. 
