16 
CENTRAL HALL. 
The adjacent case shows examples of the opposite condition, 
called melanism, depending upon an excess of dark-coloured pig- 
ment in the skin and its appendages, such as hair, feathers, etc., 
beyond what is commonly met with in the species. This is by 
no means so frequent a,s 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- 
FiG. 2. — The Somali Tsetse-Fly (Glossina longipennis). Enlarged 4 diameters 
Shows the complete closure of the wings, and the thick, straight proboscis, 
characteristic of the genus. 
duced as an example of acquired melanism, the bird having 
turned black in captivity. 
Group iUus- Another group shows that two forms of Crows which 
mediate appear quite distinct, and, judged by their external 
Forms in characters, might be regarded as different species, may in a 
Nature. ^^^^^ nature unite, and produce hybrid offspring. In 
another part of the same case is a series of Goldfinches, 
Oroup illus- 
trating 
Melanism. 
