154 TROPICAL NATURE, AND OTHER ESSAYS. 



aware of the importance of the observation of the 

 tongue ; but as the bill was so short and the tubular 

 tongue not required, there can be little doubt that the 

 organ was, at that early stage of growth, short and 

 flat, as it is in the birds most nearly allied to them. 



Differences between Sun-birds and Humming-birds. 

 In respect of all the essential and deep-seated points 

 of structure, which have been shown to offer such 

 remarkable similarities between the swifts and the 

 humming-birds, the sun-birds of the Eastern hemi- 

 sphere differ totally from the latter, while they agree 

 with the passerine birds generally, or more particularly 

 with the creepers and honey-suckers. They have a 

 deeply-notched sternum ; they have twelve tail-feathers 

 in place of ten ; they have nineteen quills in place of 

 sixteen ; and the first quill instead of being the longest 

 is the very shortest of all, while the wings are short 

 and round, instead of being excessively long and 

 pointed ; their plumage is arranged differently ; and 

 their feet are long and strong, instead of being exces- 

 sively short and weak. There remain only the super- 

 ficial characters of small size and brilliant metallic 

 colours to assimilate them with the humming-birds, 

 and one structural feature a tubular and somewhat 

 extensile tongue. This, however, is a strictly adaptive 

 character, the sun-birds feeding on small insects and 

 the nectar of flowers, just as do the humming-birds ; 

 and it is a remarkable instance of a highly peculiar 

 modification of an organ occurring independently in 

 two widely-separate groups. In the sun-birds the 

 hyoid or tongue-muscles do not extend so completely 

 over the head as they do in the humming-birds, so 



