580 THE MECHANICAL FUNCTIONS. 



whole of its external surface ; but as it retires 

 towards the root, it leaves a succession of very 

 thin pellucid membranes, in the form of cones, 

 which, when dried, form what is termed the pith 

 of the quill. The last remnant of the bulb is 

 seen in the slender ligament which passes 

 through the lower orifice, and preserves the 

 attachment of the feather to the skin. In pro- 

 cess of time, this also decays, and the whole 

 feather is cast off, preparatory to the formation 

 of another, which in due season is to replace it. 

 All the feathers are, in general, moulted annu- 

 ally, or even at shorter periods ; and the same 

 complicated process is again begun and com- 

 pleted by a new matrix produced for the oc- 

 casion, every time a new feather is to be formed. 

 It is impossible, on reviewing these curious 

 facts, not to be struck with the admirable art and 

 foresight which are implied in all this long and 

 complicated series of operations. While the 

 bird was yet nourished by the fluids of the egg, 

 the ground had already been prepared for its 

 future plumage, and for the formation of in- 

 struments of flight. A temporary investment of 

 down is in readiness to shelter the tender chicken 

 from the rude impressions of the air, and an 

 apparatus is preparing for the construction of 

 the most refined instruments for clothing and 

 for motion : first the scaffolding, as it may be 

 called, is erected, by the help of which each por- 



