16 



CENTRAL HALL. 



Group illns- 



trating 



Uelanism. 



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 

 DO 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- 



FiG. 2. — The Somali Tsetse-Flt {Glossina longipennh'). 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 Ulus- Another group shows that two forms of Crows which 

 me^fe^°**'''^PP®*^ l^^*'® distinct, and, judged by their external 



characters, might be regarded as different species, may in a 



mediate 

 Forms in 

 Nature. 



state of nature unite, and produce hybrid offspring. In 

 another part of the same case is a series of Goldfinches, 



