52 COLIN CLOUT'S CALENDAK. 



cal swifts with the longest bills and the most extensile 

 tongues would have an advantage over others, because 

 they would best be able to probe the long tubes of the 

 flowers and extract the insects from them, inside the nec- 

 tary itself. In this way the bill and tongue have grad- 

 ually grown so long in their descendants, the humming- 

 birds, that all outer resemblance to the parental swallow 

 form has been wholly lost ; and the family was, accord- 

 ingly, classed till quite recently with the externally simi- 

 lar, but genealogically quite distinct, group of sun-birds. 



In most other respects, however, the humming-birds 

 continue to resemble the ancestral swifts. The shape of 

 the wing and its proportion to the body is exactly the 

 same ; but, above all, the numerous minute anatomical 

 points of similarity settle the question at once for modern 

 biology. Even before evolutionism gave the new key 

 which solves so many of these difficult problems, it was 

 noticed that the humming-birds were very like the swal- 

 lows in many anatomical particulars, though very unlike 

 them in plumage and in the shape of the bill. Dr. Jer- 

 don, who has spent his life in studying the birds of 

 India, hesitated about ranking the sun-birds by their side 

 because of this structural community between humming- 

 birds and swallows ; but he reassured himself when he 

 looked at the general external likeness of the two tropi- 

 cal groups. lS T ow, however, we have learned that such 

 external likenesses are necessarily produced by commu- 

 nity of habit and mode of life ; while underlying struct- 

 ural resemblance forms the best test of genealogical 

 relationship. Mr. Wallace has shown conclusively that 

 the humming-birds are in reality modified swifts, and 

 that their resemblance to the Oriental sun-birds is wholly 

 due to the similarity of their circumstances. 



In fact, the habits of the two races, though much alike 



