286 CLASS viu. 



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. Thus, for instance, 

 if we compare the number of Diptera 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 certainly 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 speciea 

 from the southern part of our quarter of the earth, as the Cicadce 

 (Tettigonice FABR.) 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 

 Faunai, 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. 

 It 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), BracJiycerus, Acrydium, Mantis, 

 &c. 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 cardui, Plusia gamma, occur 

 in a considerable portion of the old world, and also in North 

 America 1 . The limits of vegetation on mountains, as well as near 



1 On the geographical distribution of Insects comp. LATEEILLE, Introduction a fa 

 Geographic generate des AracJinides et des Insectes, Mem. du Museum, iv. 1817, pp. 

 37 67; the same in Diet. Class. d'Hist. Nat. vn. 1825, pp. 290 296, and especially 

 LACOKDAIRE, Introd. a VEntoinol. n. 1833, pp. 528 619 (the best hitherto known on 

 this subject). See also C. G. BEICH, Beitray zur Lehre von der geographischen Verbrei- 



* 



