CONSIDERATION OF BRITISH BIRDS 115 
4. The absence of conspicuous colouring in 
preying birds. 
5. The absence of conspicuous colouring in 
night birds. | 
6. The association of open-nesting with 
conspicuous males. 
7. The post-nuptial change of plumage in 
the analidz and its absence in other epigamic 
coloured birds. 
8. The brighter colouring of the female in 
the Phalaropes and Dotterel. 
9. The presence of cryptic colouring in 
females and young birds. 
10. The older the bird, the more brightly 
coloured it is, as in the Gannet. 
11. The female assuming male plumage, when rendered 
sterile by disease. 
Thus can this hypothesis be applied to any 
selected material. In birds, it seems that 
protection of young is the most important 
factor in causing colour-differentiation in the 
society ; had insects been chosen, the protec- 
tion of females would have been seen to be a 
most important factor in sexual differentiation 
of colour. 
When material is considered in this way, 
that is, exhaustively, discourse is confined 
almost entirely to exceptions. A wrong im- 
