ribution, and they are comparable in that respect with the woodlice
of the genus _Platyarthrus_, to which I have already had occasion to
refer. All the species of _Claviger_ are confined to Europe, chiefly to
the south, but one species, _Cl. testaceus_, has wandered farther north
and occurs in the nest of the ant _Lasius flavus_ in the south of
England, Ireland, and Scotland. Though none of the _Clavigers_ can be
claimed as Oriental migrants, the centre of distribution of the genera
belonging to the _Clavigeridae_ is in Southern Asia, and it is probable
that the ancestors of the European _Clavigers_ have spread westward from
that region to Europe, eastward to Australia and Japan, and southward to
Madagascar and South Africa. The genus _Hopatroides_, belonging to the
same family as the so-called Spanish-fly (_Tenebrionidae_), has twelve
species in Western Asia and Greece. One only, _H. thoracicus_--an
instance of discontinuous distribution--occurs in Andalusia. _Amphicoma_
is represented in Western Asia and the Balkan peninsula by fifteen
species, while three others are met with in North-west Africa and
Southern Spain.

A genus of Dragon-fly, _Onychogomphus_, has in Europe a somewhat similar
distribution to _Claviger_, but it has besides a very extensive foreign
range. There are altogether thirty-five species; of these ten are
Holarctic, twelve Oriental, five Mascarene, and eight Ethiopian. The
centre of distribution is therefore in the Oriental region, and we may
assume that in all probability the genus has originated there, the
European species having travelled west with the Oriental migration at an
early date of the Tertiary Era.

_Ryothemis_, another genus of Dragon-flies, has originated perhaps
somewhat farther east than the last, for no less than thirteen species
are found in Australia, a like number in India, five in Madagascar and
Africa, and five in the Holarctic region. Both of these genera are
entirely absent from America, and they have possibly travelled to Europe
together.

Among the European _Orthoptera_--the group to which our Earwigs and
Grasshoppers belong--there are also a good many instances of Oriental
migrants. One of the most striking of these is the curious "praying
insect" (_Mantis religiosa_). It occurs all over Southern Europe, and
ranges as far north as the north of France. It is also found in Southern
Germany and in Austria, and has a vast extra-European range. There are
even records of its