388 
REVIEWS. 
driven to great straits as regards liis mental food, when, as he tells 
ns, he took to reading the Athenaeum three times over—“ the first 
“ time devouring the more interesting articles—the second, the whole 
“ of the remainder—and the third, reading all the advertisements, 
“from beginning to end!” 
Ega was, indeed, as Mr. Bates remarks, a fine field for a Natural 
History Collector, the only previous scientific visitants to that region 
having been the German Naturalists Spix and Martius, and the Count 
de Castelnau when he descended the Amazons from the Pacific. Mr. 
Bates’ account of the Monkeys of the genera Brachyurus and Nycti- 
pithecus and Midas met with in this region, and the whole of the very 
pregnant remarks which follow on the American forms of the Quadru- 
mana will he read with interest by every one, particularly by those 
who pay attention to the important subject of geographical distribu¬ 
tion. We need hardly say that Mr. Bates, after the attention he 
has bestowed upon this question, is a zealous advocate of the hypo¬ 
thesis of the origin of species by derivation from a common stock. 
After giving an outline of the general distribution of Monkeys, he 
clearly argues that unless the “ common origin at least of the species 
“of a family be admitted, the problem of their distribution must 
“ remain an inexplicable mystery.” Mr. Bates evidently thoroughly 
understands the nature of this interesting problem, and in another 
passage in which the very singular distribution of the Butterflies of 
the genus Heliconius is enlarged upon, concludes with the following 
significant remarks upon this important subject: — 
“ In the controversy which is being waged amongst Naturalists since the pub¬ 
lication of the Darwinian theory of the origin of species, it has been rightly said that 
no proof at present existed of the production of a physiological species, that is, a 
form which will not interbreed with the one from which it was derived, although 
given ample opportunities of doing so, and does not exhibit signs of reverting to its 
parent form when placed under the same conditions with it. Morphological species, 
that is, forms which differ to an amount that would justify their being considered 
good species, have been produced in plenty through selection by man out of variations 
arising under domestication or cultivation. The facts just given are therefore of 
some scientific importance, for they tend to show that a physiological species can be 
and is produced in nature out of the varieties of a pre-existing closely allied one. 
This is not an isolated case, for I observed in the course of my travels a number of 
similar instances. But in very few has it happened that the species which clearly 
appears to be the parent, co-exists with one that has been evidently derived from it. 
Generally the supposed parent also seems to have been modified, and then the 
demonstration is not so clear, for some of the links in the chain of variation are 
wanting. The process of origination of a species in nature as it takes place succes¬ 
sively, must be ever, perhaps, beyond man’s power to trace, on account of the great 
lapse of time it requires. • But we can obtain a fair view of it by tracing a variable 
and far-spreading species over the wide area of its present distribution; and a long 
observation of such will lead to the conclusion that new species must in all cases 
have arisen out of variable and widely-disseminated forms. It sometimes happens, 
as in the present instance, that we find in one locality a species under a certain form 
which is constant to all the individuals concerned ; in another exhibiting numerous 
varieties ; and in a third presenting itself as a constant form quite distinct from the 
one we set out with. If we meet with any two of these modifications living side by 
side, and maintaining their distinctive characters under such circumstances, the 
proof of the natural origination of a species is complete ; it could not be much more 
