286 CLASS VIII. 
nay, whole orders of insects, have been collected in other parts 
of the world with more or less of inadvertency by travellers and 
collectors, or at least not with such care as to allow us to deduce 
from the species yet known any general rules. ‘T'hus, for instance, 
if we compare the number of Déptera found out of Europe with the 
European, and thus form a measure of the proportion which sub- 
sists between exotic and European species, we shall arrive at a 
conclusion which will certamly vary much from the truth. Some 
genera are proper to the warm regions of the earth alone, and in 
Europe are represented either not at all or only by a few species 
from the southern part of our quarter of the earth, as the Cicade 
(Tettigonie Far.) and the genus Phasma. On the whole our 
knowledge of some orders of insects, especially of the Hemiptera 
and Orthoptera, would be very confined, were we to limit ourselves 
to European insects. The distribution of the same or very similar 
species in countries widely distant from each other, the remarkable 
richness of the same natural group giving a special character to 
Faune, often depends upon the same quality of the soil and a 
resemblance in the vegetation. Thus for instance the insects of the 
sandy regions of Asia near the Caspian Sea correspond to those of 
North Africa, nay even to those of the Colony at the Cape. A 
similar remark may be made in relation to the class of Mammalia. 
Tt is this remarkable abundance of certain forms which leads us 
at first sight, and even without having determined a single species, 
to distinguish a collection of insects from the Cape of Good Hope, 
for instance, from one from the Indian Archipelago; Mylabris, 
Pimelia (Trachynotus, Sepidium), Brachycerus, Acrydium, Mantis, 
&e. in the first, Phasma, Pentatoma, numerous resplendently coloured 
Papiliones in. the second, give to the two a totally different appear- 
ance. Some species of insects are confined within very narrow 
limits; others, as for instance, Papilio cardut, Plusia gamma, occur 
in a considerable portion of the old world, and also in North 
America!.—The limits of vegetation on mountains, as well as near 
1 On the geographical distribution of Insects comp. LaTREILLE, Introduction & la 
Géographie générale des Arachnides et des Insectes, Mém. du Muséum, Iv. 1817, pp. 
37—67; the same in Dict. Class. d’Hist. Nat. vit. 1825, pp. 290—296, and especially 
LacorpaireE, Introd. & UEntomol. 11. 1833, pp. 528—619 (the best hitherto known on 
this subject). See also C.G. Ruicn, Beitrag zur Lehre von der geographischen Verbrei- 
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