of Edinburgh, Session 1864-65. 277 
method which has been followed in the introduction of new forms. 
Let us test this question by bringing to bear upon it some particu- 
lar example of specific variation. I select for this purpose one 
example to which my attention has been lately directed, wbicli 
will illustrate what I mean better than any abstract discussion. 
It is the case of the Humming-birds. 
This group of birds seems to me to exhibit, in the most striking 
form, not a few of those mysteries of creation which at once tempt 
us to speculate on the origin of species, and at the same time con- 
found every endeavour to bring it into relation with any process 
which we know or can conceive. In the first place, they are shar})ly 
defined from all other forms in that class of the animal kingdom to 
which they belong. It is most difficult to say what is their nearest 
affinity, and the nearest, when it is found, is very distant. Secondly, 
they are absolutely confined to one continent of the globe. In 
the third place, the various species as amongst themselves are 
very closely united, ranging indeed over a great variety of forms, 
but for the most part connected with each other by very nice grada- 
tions. In the fourth place, there are, so to speak, some gaps in the 
scale, which suggest that some species have either been lost, or 
have not yet been discovered. In the fifth place, each of these 
species, however nearly allied to some other, appears to be absolutely 
fixed and constant, there being not the slightest indication of any 
mixture — of any hybrid forms. In the sixth place, there is the most 
wonderful adaptation of special organs for the performance of 
special functions, and for the relation of these organs to particular 
structures in the vegetable kingdom. In the seventh place, there is 
a development, for which in extent and variety there is no parallel 
in the world, of structures designed for mere ornament, and entirely 
separate from any other known or conceivable use. 
A few words on some of these characters will show their separate 
and joint bearing on the idea of Creation by Law. 
In the first place, then, the absolute distinctiveness from all 
others of this family of birds, coupled with its immense extent, 
gives the idea of some common bond, some physical cause, to which 
such an identity in physical characters must be due. This identity 
prevails not only in such essential matters as the structure of the 
bill and tongue, in the form of the feet and of the wings, in the habits 
