The geographical distribution of animals, with a study of the relations ...

212 ZOOLOGICAL GEOGRAPHY. [part hi.immigration across the ocean, in various ways and during a longperiod. These deficiencies are, on the other hand, quite inconsistentwith the theory (still held by some entomologists) thata land communication is absolutely necessary to account forthe origin of the Madeiran fauna.First, then, we can understand how the tiger-beetles (Cicindelidae)are absent ; since they are insects which have a short weakflight, but yet to whom flight is necessary. If a few had beenblown over to Madeira, they would soon have become exterminated.The same thing applies to the Melolonthidse, Cetoniidse,Eumolpidae, and Galerucidse,—all flower and foliagehauntinginsects, yet bulky and of comparatively feeble powersof flight.Again, all the large genera abundant in South Europe,which have been mentioned above as absent from Madeira,wholly apterous (or without wings), and thus their absence is amost significant fact ; for it proves that in the case of all insectsof moderate size, flight was essential to their reaching the island,which could not have been the case had there been a land connection.There are, however, one or two curious exceptions tothe absence of these wholly apterous European genera in Madeira,and as in each case the reason of their being exceptions canbe pointed out, they are eminently exceptions that prove therule. Two of the apterous species common to Europe andMadeira are found always in ants' nests ; and as ants, whenwinged, fly in great swarms and are carried by the wind togreat distances, they may have conveyed the minute eggs ofthese very small beetles. Two European species of Blapsoccur in Madeira, but these are house beetles, and are admittedto have been introduced by man. There are also three speciesof Meloe, of which two are European and one peculiar.These are large, sluggish, wingless insects, but they have amost extraordinary and exceptional metamorphosis, the larvaein the first state being minute active insects parasitic on bees,and thus easily conveyed across the ocean. This case is mostsuggestive, as itareaccounts for what would be otherwise a difficultanomaly. Another case, not quite so easily explained, is thatof thegenus Acalles, which is very abundant in all the Atlantic