48 
ZOOLOGICAL GEOGRAPHY. 
[part m. 
number and variety of the tropical forms has given them the ad- 
vantage. Thus we find that among the Lucanidse, Buprestidse, and 
Longicorns, the northern element is hardly perceptible. Most of 
these are either purely Neotropical, or allied to Neotropical genera, 
with the admixture, however, of a decided Australian element. 
As in the case of the Amphibia and fresh-water fishes, the Aus- 
tralian affinity, as shown by insects, is of two kinds, near and 
remote. We have a few genera common to the two countries ; 
but more commonly the genera are very distinct, and the affinity 
is shown by the genera of both countries belonging to a group 
peculiar to them, but which may be of very great age. In the 
former case, we must impute some of the resemblance of the two 
faunas to an actual interchange of forms within the epoch of 
existing genera— a period of vast and unknown duration in the 
class of insects ; while in the latter case, and perhaps also in 
many of the former, it seems more in accordance with the whole 
of the phenomena, to look upon most of the instances as 
survivals, in the two southern temperate areas, of the relics of 
groups which had once a much wider distribution. That this is 
the true explanation, is suggested by the numerous cases of dis- 
continuous and scattered distribution we have had to notice, in 
which every part of the globe, without exception, is implicated ; 
and there is a reason why these survivals should be rather more 
frequent in Australia and temperate South America, inasmuch 
as these two areas agree in the absence of a considerable number 
of otherwise cosmopolitan vertebrate types, and are also in many 
respects very similar in climatic and other physical conditions. 
The preponderating influence of the organic over the physical 
environment, as taught by Mr. Darwin, leads us to give most 
weight to the first of the above-mentioned causes ; to which we 
may also impute such undoubted cases of survival of ancient 
types as the Cente tides of the Antilles and Madagascar— both 
areas strikingly deficient in the higher vertebrate forms. The 
probable mode and time of the cross migration between Australia 
and South America, has been sufficiently discussed in our chapter 
on the Australian region, when treating of the origin and affinities 
of the New Zealand fauna. 
