STRUCTURE OF BIRDS 



Early vertebrates turned their hands to flying, 

 to such good purpose that ultimately the hand 

 became transformed into a wing, and in the bird 

 three fingers were sacrificed. It is imperative 

 that the texture of the wings be smooth and 

 yielding. The " leather wings " of the bat and 

 the rainbow-like pinions of the dragon-fly are 

 formed of membrane, transparent and gauzy in 

 the latter, brown and opaque in the former. 

 The butterfly and the bird protect their wings 

 with a covering of scales and feathers, both 

 arranged on the over-lapping principle, like the 

 tiles on a roof, being attached at their bases to 

 the wing, but having the extremities free. This 

 feather covering gives the bird's wing an immense 

 superiority over the bat's for if a feather or two 

 be injured it can be replaced, whereas an injury 

 to a bat's wing involves total disablement. The 

 difference is akin to that between a window formed 

 of many small panes and one consisting of a single 

 sheet of glass. The fragility of the dragon- 

 fly's wing may be the reason why it is equipped 

 with four. We recently released a home-bred 

 dragon-fly in the garden. A few days later it 

 was re-caught, one of the wings having been torn 

 right ofl from the base. Still, the insect was able 

 to fly, and to maintain a tolerably straight course 

 for a short distance. 



Winged creatures differ considerably in their 

 manner of disposing their pinions when at rest. 

 In butterflies, the wings are closed over the back, 

 making them inconspicuous from above. They 

 usually adopt a slightly sideways attitude in 

 order — it has been tentatively suggested — to re- 

 duce the shadow. It may be readily seen that 

 if the butterfly leant over sufficiently towards 

 the sun, the shadow would disappear altogether. 

 Such a habit could not fail to be a great pro- 



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