1864. | Barus’s Naturalist on the Amazons. 189 
stated by Mr. Bates, as a most beautiful proof of the theory of natural 
selection, by showing that a new adaptation, or the formation of a new 
species is not effected by a great and sudden change, but by numerous 
small steps of natural variation and selection. Local conditions favour 
the increase of one or more varicties in a district at the expense of the 
others,—the selected ones being different in different districts, in the 
case of the varieties of Mechanitis. ‘“ With the mimetic species Leptalis 
Theonoe the case is different. We see here a segregation of local forms 
sunilar to that of Mechanitis Polymnia ; but we believe we know the con- 
ditions of life of the species, and find that they vary from one locality 
to another. The existence of the species, in each locality, is seen to 
depend on its form and colours, or dress being assimilated to those of 
Ithomice of the same district, such assimilation being apparently its 
only means of escaping extermination by insectivorous animals.” And 
indeed the abundance of the mocked species seems to show that it pos- 
sesses some such immunity, and at all events lives under conditions 
very favourable to its increase and preservation. To exist in a certain 
locality, a Leptalis must wear a certain dress, and those of its varieties 
which do not come up to the mark are rigidly sacrificed. 
It is manifestly impossible in a review to enter fully into all 
the arguments of the work. All that can be done is to indicate the 
salient points, and abstract the conclusions; and much as these specu- 
lations of Mr. Bates have interested us, we must content ourselves with 
this imperfect résumé of them, and refer those who would know more 
upon the subject to the memoir itself. In taking leave of Mr. Bates, 
however, we cannot help expressing the gratification and rare pleasure 
we have felt in the perusal of his ‘ Naturalist on the Amazons,’ in which 
a vast amount of truthful and original information is given, in an 
unobtrusive and unselfish style. The world of naturalists is under a 
heavy obligation to him for his toilsome and laborious collection of 
facts, and for the interesting, though probably not less laborious, work 
in which they are permanently embodied. Nor must we omit thanks 
to Mr. Darwin, for screwing Mr. Bates’s courage to the sticking place, 
without which perhaps the work would never have been written, or at 
all events have been so deferred as to impair its value. The ‘ Contribu- 
tions to Insect Fauna of the Amazons’ are an important addition to 
Entomological science, and however averse some may be to the theory of 
natural selection, no one can fail to be instructed, as well as interested, 
by the ingenious remarks with which Mr. Bates preludes the systema- 
tic part of the subject. We hail Mr. Bates as a worthy naturalist- 
traveller, and willingly and gratefully accord to him a well-earned and 
high position amongst those who have advanced science by patient, 
earnest, and original investigation. 
