70 THE ZOOLOGIST. 
It was probably owing to the separation of North from South 
America, at that period, that the complete extinction of the 
Proboscidea, Equide, Rhinocerotide, and other Ungulata was 
there effected. These animals were probably driven south by 
the cold, and, not having a large southern continent to retreat to, 
were completely exterminated. The existing Tapiride are the 
only descendants amongst the Pertssodactyla that exist in the 
Neotropical Region at the present day, none being now found in 
the Nearctic Region. 
Amongst insects, Mr. Wallace has wisely confined his attention 
to the groups best known, as the Rhopalocerous Lepidoptera 
and the more showy amongst the Coleoptera, because these 
alone have been sufficiently studied to afford adequate material for 
generalization. Mr. Wallace has a singular power of suggesting 
an explanation of a difficulty, and this is well shown in his 
observations on the occurrence of numerous insects in South 
Temperate America which belong to genera found otherwise in 
north temperate regions only. Amongst the diurnal Lepi- 
doptera, for instance, species of the genera Hipparchia, Argynnis, 
and Colias, and several genera allied to Evrebia, are found in 
South Temperate America, and form a sufficiently remarkable 
group of northern forms, to render an explanation of their 
origin necessary. Mr. Wallace, indeed, admits that both in 
diurnal Lepidoptera and in Carabide, the northern element 
is fully equal to the tropical, if it does not preponderate over it. 
The whole of his argument is too long to be here extracted, 
but he points out that the great mass of neotropical butterflies 
are forest species, and for countless ages have been developed 
in a forest-clad tropical country. The north temperate butter- 
flies, on the other hand, are for the most part species frequenting 
the open country, haunting pastures, mountains, and plains, 
and often wandering .over an extensive area. These would 
find in the higher slopes of the mountains vegetation and conditions 
suited to them, and would occupy such stations in less time than 
would be required to adapt and modify the forest-haunting groups 
found in the American lowlands. It should not be forgotten, also, 
that along the higher regions of the Andes there is an almost con- 
tinuous temperate region, which would provide for the animals of 
Northern Temperate America a district along which they could pass 
through Tropical America into the cooler regions of the south. 
