250 



CHAPTERS ON EVOLUTION. 



FIG. 167. SWIFTS. 



of the beak of a swallow or swift slightly lengthened. Thinking 

 (erroneously) that the young birds were fed by their parents on 

 honey, I tried to feed them with a syrup made of honey and water ; 



but though they kept their 

 mouths constantly open, 

 as if ravenously hungry, 

 they would not swallow 

 the liquid, but threw it 

 out again, and sometimes 

 nearly choked themselves 

 in the effort. At length 

 I caught some minute 

 flies, and on dropping 

 one of these into the 

 open mouth it instantly 

 closed, the fly was gulped 

 down, and the mouth 

 opened again for more : 

 and each took in this way 

 fifteen or twenty little flies in succession before it was satisfied. 

 They lived thus three or four days, but required more constant care 

 than I could give them. These little birds were in the swift stage ; 



they were pure insect-eaters, 

 with a bill and mouth adapted 

 for insect-eating only." 



Such an interesting recital 

 once again illustrates the 

 maxim, that the likeness be- 

 tween living beings, imper- 

 ceptible in the adult stage, 

 may yet be plainly enough 

 apparent in the earlier phases 

 of development. As with the 

 crustaceans, where we find a 

 shrimp and a barnacle, utterly 

 unlike as adults, beginning life 

 under an essentially similar 

 guise, so with the swifts and 

 humming-birds their like- 

 nesses, masked by differences 

 in habits of life, are neverthe- 

 less traceable without difficulty 

 in the young state. Mr. Wallace especially reminds us that certain 

 of the sun-birds themselves, resemble the humming-birds in respect 

 of their long bills and tubular tongue, adapted, like those of the 



FIG. 168. SUN-BIRD. 



