CHILE AND CALIFORNIA 
413 
any South American forms. The genus of Tenehrionidae 
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, R., “Insect Fauna of Chile,” p. 162. 
f Wallace, A. R., “ Geographical Distribution,” Yol. II., p. 45. 
