344 ANIMALS OF NEIGHBOURHOOD OF EGA. Cuap. XII. 
America from the continental mass of the Old World, before the 
Pithecidz originated. But, if these explanations, founded on natural 
causes, be entertained, we commit ourselves, by the fact of entertaining 
them, to the admission that natural causes are competent to explain the 
existence or non-existence of forms in a given area; and why may not 
the exercise of our reason, founded on carefully observed and collated 
facts, be carried a step farther, namely to the origin of the species of 
monkeys themselves? I have already shown how singularly species of 
monkeys vary in different localities, and have given the striking case of 
the white and red-haired Uakaris. If these two forms, which are 
considered by the most eminent naturalists as distinct species, have 
originated, as the facts of their distribution plainly tell us they have, 
from one and the same stock, why may not the various species of 
Lemurs, of Baboons, of Gibbons, and so forth, given the necessary 
amount of time and climatal changes, have originated in the same way ? 
And if we can thus account for the origin of the species of one genus, 
on what grounds can we deny that the genera of the same family, or the 
families of the same order, have also proceeded from a common stock ? 
I throw out these suggestions simply for the consideration of thoughtful 
readers, but must add, that unless the common origin, at least, of the 
species of a family be admitted, the problem of the distribution of 
monkeys over the earth’s surface must remain an inexplicable mystery, 
whilst, if admitted, a flood of light illuminates the subject, and promises 
an early solution to honest and patient investigation. These questions, 
also, show how interesting and difficult are the problems which Natural 
History, granted the right and ability of the human mind to deal with 
them, has to solve. 
It is a suggestive fact that all the fossil monkeys which have been 
found in Europe and America belong in each case to the types which 
are still peculiar to the continent which they inhabit. The European 
fossils are ali of the Pithecidz family, the South American all belong 
to the Cebide and Marmoset families. The separation of the two 
continental masses (at least of their warm zones) must therefore be of 
great geological antiquity. It is interesting to trace how the diversifica- 
tion of forms (if the expression may be allowed), since the separation, 
has gone on in Tropical America. What wide divergence as to size, 
forms, habits, and mental dispositions, between the silver marmoset so 
small that it may be inclosed in the two hands, and the strong and 
savage black Howler, nearly two feet and a half in length of trunk! 
Yet there has been no direct advance in the organisation of the order 
towards a higher type, such as is exhibited inthe Old World. America, 
for her share, has produced the most perfectly arboreal monkey in the 
world ; but beyond the perfection of the arboreal type she does not go. 
The retention of arboreal forms throughout long geological ages may 
teach geologists that there must always have been extensive land areas 
covered by forests on the site of the tropical zone of America. It is 
curious to reflect, in conjunction with the fact of the advance of the 
American Quadrumana having halted at a low stage, that ethnologists 
have almost unanimously come to the conclusion that the race of men 
now inhabiting the American continent are not Autochthones of America 
