212 
ZOOLOGICAL GEOGRAPHY. 
[part in. 
immigration across the ocean, in various ways and during a long 
period. These deficiencies are, on the other hand, quite incon- 
sistent with the theory (still held by some entomologists) that 
a land communication is absolutely necessary to account for 
the origin of the Madeiran fauna. 
First, then, we can understand how the tiger-beetles (Gicinde- 
lidse) are absent; since they are insects which have a short weak 
flight, but yet to whom flight is necessary. If a few had been 
blown over to Madeira, they would soon have become exter- 
minated. The same thing applies to the Melolonthidse, Ceto- 
niidae, Eumolpidse, and Galerucidas, — all flower and foliage- 
haunting insects, yet bulky and of comparatively feeble powers 
of flight. Again, all the large genera abundant in South Europe, 
which have been mentioned above as absent from Madeira, are 
wholly apterous (or without wings), and thus their absence is a 
most significant fact ; for it proves that in the case of all insects 
of moderate size, flight was essential to their reaching the island, 
which could not have been the case had there been a land con- 
nection. There are, however, one or two curious exceptions to 
the absence of these wholly apterous European genera in Madeira, 
and as in each case the reason of tlieir being exceptions can 
be pointed out, they are eminently exceptions that prove the 
rule. Two of the apterous species common to Europe and 
Madeira are found always in ants’ nests ; and as ants, when 
winged, fly in great swarms and are carried by the wind to 
great distances, they may have conveyed the minute eggs of 
these very small beetles. Two European species of Elays 
occur in Madeira, but these are house beetles, and are admitted 
to have been introduced by man. There are also three species 
of Mdoe, of which two are European and one peculiar. 
These are large, sluggish, wingless insects, but they have a 
most extraordinary and exceptional metamorphosis, the larvae 
in the first state being minute active insects parasitic on bees, 
and thus easily conveyed across the ocean. This case is most 
suggestive, as it accounts for what would be otherwise a difficult 
anomaly. Another case, not quite so easily explained, is that 
of the genus Acalles , which is very abundant in all the Atlantic 
