4 
VERTEBRATA. 
THE IMPERIAL EAGLE : ILLUSTEAnON OP THE PLDMAGB OF BIRDS, 
impossible with many exotic birds, that such mistakes as these can be prevented or rectified. 
Another fertile source of similar errors is to be found in the difference which very commonly ex- 
ists between the two sexes, a difference which is often so great that, without particular informa- 
tion derived from the observation of the birds in their native haunts, it would be impossible to 
refer the males and females to their proper partners ; and the difficulty is still further increased by 
the fact that the young of all birds in their first plumage difier more or less fi"om their parents, 
