August 



of the latest layers. Although this bird more com- 

 monly builds its nest in banks, I have not unfre- 

 quently found it in thorn hedges, and the one shown 

 in the picture was so placed. At the time of photo- 

 graphing it August 1 6 there were in the nest two 

 young birds, evidently hatched about a couple of days 

 before ; and an egg of a plain white ground, and 

 almost without markings, thus differing considerably 

 from the usual purplish-white ground and numerous 

 streaks of the normal egg. I have noticed that 

 eggs laid late in the year often present some 

 abnormality, and that eggs under such condi- 

 tions showing abnormal features often addle. The 

 picture referred to in other respects of indifferent 

 value is interesting as illustrating the obsolete 

 function of a rudimentary thumb, which in the 

 course of evolution has been transformed into the 

 winglet. 



As is well known, the wing in birds corresponds 

 with the fore-limb in mammals, and the feathers at 

 the ends of the wings are arranged upon a sub- 

 structure consisting of two surviving fingers and a 

 thumb of an organ which, in the bird's remote 

 ancestors, must to some extent have served the 

 purposes of a hand. The two other fingers have 

 been wholly lost. The small thumb provides the 

 support for the feathers of the winglet or bastard 

 wing, which lies at the bend in the middle on 

 the outer side of a bird's wing. Before birds 

 are fledged these finger-like structures are readily 



273 T 



