52 COLIN CLOUT'S CALENDAR. 



the field in the small portion of Africa and Asia fitted 

 for the evolution of such a race as the humming-birds, 

 and may thus effectually have prevented the eastern 

 swifts from ever developing in that direction. Of course 

 in any case the specialisation of humming-birds in 

 America must date back to a very remote period, both 

 on account of the profound modifications their form has 

 undergone, and on account of the immense number of 

 genera and species into which they have split up. 



