INTRODUCTORY COLLECTION. 
25 
the butterfly {Kallima inacJiis), when its wings are closed, could 
not be surpassed. A further stage of the same condition, called 
" Mimicry," is where the object resembled, or mimicked, is an- 
other living animal, belonging to a different species, family, or 
even order. The resemblance in these cases is also believed to 
be for protection, or to be in some way advantageous to the 
animal possessing it. We know, however, so little of the 
habits and life-history of animals in a state of nature that 
many of the purposes supposed to be served by particular 
colours or appearances can only be regarded at present as con- 
jectural. Whatever be the real explanation, the facts shown by 
the specimens in this case are very curious, and well worthy of 
careful consideration. 
The next case contains a series of specimens illustrating a^6i7zi^sm, Group iiius- 
a condition in which the pigment or colouring matter, usually ^^^^^j^ 
present in the tissues constituting the external covering of the 
body, and which gives them their characteristic hue, is absent. 
Individuals in this condition occur among many animals of 
various kinds, and are called " albinos." In some of the speci- 
mens shown in the case the albinism is complete, but in many 
it is partial, the absence of colouring matter being limited to 
portions of the surface only. 
An eighth case shows examples of the opposite condition, Group iiius- 
called melanism, depending upon an excess of dark-coloured ^gj^n^. 
pigment in the skin and its appendages, the hair, feathers, etc., 
beyond what is normally met with in the species. This is by 
no means so frequent as albinism. A black Leopard in the 
middle of the case is a good illustration. It is not a distinct • 
species, but an individual variety of the common Leopard, born 
from parents of the normal colour. A black Bullfinch is intro- 
duced as an example of acquired melanism, the bird ha\T.ng 
turned black in captivity. 
The last group shows that two forms of Crows which appear Group illus- 
quite distinct, and which, judged by their external characters, ^^J^^^^^^®^" 
might be held to be different species, may in a state of nature Forms in 
unite, and produce offspring of a perfectly intermediate cha- . 
racter. In the same case is also a series of Goldfinches, showing 
a complete gradation between birds of different coloration, and 
which have naturally been held to be different species. Both 
