NOTES ON THE GEOGRAPHICAL DISTRIBUTION OF ANIMALS. 267 
(Wallace, “ G-eogr. Distr.” i. p. 273). The insects of Madagascar, 
however, are closely allied to existing African species, and many 
■of the most remarkable, formerly supposed to be peculiar to the 
island, have since been received from Natal or Zanzibar. There 
is also a considerable resemblance between the Mascarene 
-fauna, and that of distant parts of the world, in which connec- 
tion we may refer to the numerous traditions, previously men- 
tioned, of recent subsidences in various parts of the Indian 
Ocean. 
As a rule, competition is far more severe on continents than 
on islands ; hence the great number of peculiar forms which 
survive in islands, though long superseded on continents, and it 
appears that according to this principle, the insects of Mada- 
gascar have become less strongly modified than those of the 
African Continent, and therefore represent to some extent a 
more ancient fauna. A remarkable case is afforded by two 
pairs of butterflies, inhabiting different parts of the world. One 
is Papilis Merope , a large black and white butterfly, with tails 
on the hind wings, found all over Tropical Africa, and varying 
considerably in different localities. The females are altogether 
unlike the male, being without a tail, and of a totally different 
shape and colour, resembling butterflies of other groups, which 
are protected from birds, &c., by their nauseous odour. But 
P. Merope is represented in Madagascar by P. Meriones , the 
female of which only differs from the male in the presence of 
an additional black bar on the fore wings. The other example 
is that of Argynnis Niphe , a common Indian species, which is 
tawny, with black spots, and the female of which has the tips 
of the forewings broadly dusky, with a black bar across them, 
giving it a great resemblance to Danaus Chrysippus, a widely 
distributed insect, which is “ mimicked ” in the same way by 
the females of several other butterflies besides A. Niphe , even 
including one of the female varieties of Papilio Merope , 
already referred to. But the Australian representative of A. 
Niphe (A . inconstans ), though differing so little from the male 
■of A. Niphe that it was long considered to be no more than a 
slight local variety, has the sexes alike, the female having no 
white bar on the wings, although a small Danaus (D. Petilia ), 
■closely allied to P. Chrysippus , is also found in Australia. 
Turning to the Oriental Region, we find that North India is 
much richer in species than the south. This is partly owing to 
the greater variety of elevation (just as the southern peninsulas 
of Europe are poorer in species than the districts in which the 
-central ranges lie*), but not entirely, since many North Indian 
* Andalusia scarcely produces more species of butterflies than Sweden ; 
Austria, Switzerland, or South France have nearly twice as many. 
