MEMBRA CIDJE. 
263 
insects is world-wide, and that it is not connected primarily with temperature or 
climate. 
Zoological distribution is not controlled so much by the latitude as by the longitude 
of the globe, that is, it follows more the Isothermal lines which often may govern the 
vegetation which sustains the particular life of the animals of those regions. 
Climate is by no means the chief factor. Geological disturbances and geogra¬ 
phical formations cause the upheaval or formation of mountain chains, of wide deserts, 
dense forests, and ocean currents with their attendant winds. These are more 
effective isolators of animal life than the cold climates of even high latitudes. 
Ancient geology tells us very little of the age of Membracidse, but we may 
surmise that Asia was their primitive centre, but if so, their spread into America 
(now their chief home) probably was from the North, at a time when the ape lived, and 
the palm-tree flourished in Greenland. This might appear to be the more probable 
conjecture, since the fauna of America, north of Mexico, point to a colonisation from 
the more temperate regions of Asia, subsequent to the glacial period. 
The Hemiptera were one of the earliest denizens of our earth, and they might 
have been driven southwards as the great ice cap of America descended, the 
cold of which doubtless reduced, but did not destroy the genera or their affinities 
then existing. Many of these were of the great Palsearctic region. 
In Asia the distribution of Membracidse might be from Siberia through China; 
and from the Malay Peninsula to India and Borneo. 
In Africa the occurrence of Centrotidse is known from Calabar on the West, to 
Abyssinia and Natal on the East, and to the Cape of Good Hope in the South. In 
America their range is from Canada to Panama, and thence through Brazil and 
Ecuador almost to Patagonia in the South. Australia and New Zealand are duly 
represented, and also the distant Philippine Isles and New Guinea. 
The comparative isolation of Europe from the rest of the world as regards the 
Membracidse is remarkable. The great Ural and Caucasian chains of mountains 
seem to have been effective barriers through geological epochs, with the singular 
exception of three species of Centrotidse. 
But even comparatively narrow sea straits may separate the fauna of two dis¬ 
tributary districts. Thus the straits between Baly and Lombock are only in one 
part ten miles wide, yet the insects show that the Indo-Malayan region is distinct 
from the Austro-Malayan on the opposite side. (/See Wallace’s “ Malay Archipelago,” 
chap. i.). 
There would appear to be less competition and struggle for life on islands than 
on the mainland, yet such is not the invariable rule. The Membracidse of the 
Philippines, Sumatra, and Ceylon do not show a higher development in size than 
