CHILE AND CALIFOKNIA 413 



any South American forms. The genus of Tenebrionidae 

 Apocrypha is quite confined to California and Chile. That 

 all these instances indicate the existence of a former direct 

 land connection between Chile and California, independent 

 of the rest of South America, as I have explained before, is 

 indicated by another example derived from the same family 

 of beetles. The three closely allied genera Arthrocomus, 

 Stomion and Eurymetopon occur respectively in Chile, the 

 Galapagos islands and California. 



Under this heading also comes an instance of distribution 

 which had not hitherto been noted and which was pointed out 

 by Mr. McLachlan.* He remarked that the family Limno- 

 philidae, a family of insects the larvae of which manufacture 

 those cases of twigs and straws, so abundant in northern 

 ponds and ditches, is not known to occur south of Mexico, 

 except in Chile and the Falkland islands. 



It was Dr. Wallace,f I believe, who first drew attention, 

 as already noted in a previous chapter (p. 235), to the 

 remarkable fact that a large number of European and North 

 American genera, such as the butterfly Argynnis and the 

 running beetle Carabus, reappeared far south of the tropics 

 in Chile, Argentina and Tierra del Fuego. I also alluded 

 to his explanation of the manner in which this surprising 

 phenomenon had been brought about. He was under the im- 

 pression that this migration across the tropics had been 

 effected mainly during successive Glacial Epochs, when the 

 mountain range of the isthmus of Panama, if moderately in- 

 creased in height, might have become adapted for the passage 

 of northern forms, while storms would often carry insects 

 from peak to peak over intervening forest lowlands or narrow 

 straits of sea. Improbable as this theory may appear, it might 

 still be defended as long as we had to deal merely with the 

 occurrence in southern South America of a few northern 

 insects. But the phenomenon is, as we have seen, a much 

 more widespread one. It applies to earthworms, slugs, sala- 

 manders and even mammals, and it is evidently the result 

 of a dispersal which occurred long before the Glacial Epoch. 



* McLachlan, E., "Insect Fauna of Chile," p. 162. 



f Wallace, A. E., " Geographical Distribution," Vol. II., p. 45. 



