ous danger by not using them, and the wings therefore became reduced
or were completely lost. But when they were essential they were enlarged
and strengthened, so that the insect could battle against the winds and
save itself from destruction at sea. Many flying insects, not varying
fast enough, would be destroyed before they could establish themselves,
and thus we may explain the total absence from Madeira of several whole
families of winged insects which must have had many opportunities of
reaching the islands. Such are the large groups of the tiger-beetles
(Cicindelidae), the chafers (Melolonthidae), the click-beetles
(Elateridae), and many others.

But the most curious and striking confirmation of this portion of Mr.
Darwin's theory is afforded by the case of Kerguelen Island. This island
was visited by the _Transit of Venus_ expedition. It is one of the
stormiest places on the globe, being subject to almost perpetual gales,
while, there being no wood, it is almost entirely without shelter. The
Rev. A.E. Eaton, an experienced entomologist, was naturalist to the
expedition, and he assiduously collected the few insects that were to be
found. All were incapable of flight, and most of them entirely without
wings. They included a moth, several flies, and numerous beetles. As
these insects could hardly have reached the islands in a wingless state,
even if there were any other known land inhabited by them--which there
is not--we must assume that, like the Madeiran insects, they were
originally winged, and lost their power of flight because its possession
was injurious to them.

It is no doubt due to the same cause that some butterflies on small and
exposed islands have their wings reduced in size, as is strikingly the
case with the small tortoise-shell butterfly (Vanessa urticae)
inhabiting the Isle of Man, which is only about half the size of the
same species in England or Ireland; and Mr. Wollaston notes that Vanessa
callirhoe--a closely allied South European form of our red-admiral
butterfly--is permanently smaller in the small and bare island of Porto
Santo than in the larger and more wooded adjacent island of Madeira.

A very good example of comparatively recent divergence of character, in
accordance with new conditions of life, is afforded by our red grouse.
This bird, the Lagopus scoticus of naturalists, is entirely confined to
the British Isles. It is, however, very closely allied to the willow
grouse (Lagopus al