THE SKIN AND ITS APPENDAGES 109 



developed and from which it has derived its 

 nourishment, is withdrawn from the cavity 

 of the quill, and the inferior umbilicus is 

 plugged by some of the conical scales which 

 occupy the interior of the quill. When the 

 time comes for the old feathers to be moulted, 

 the feather -follicle again becomes active. A 

 new feather is formed and pushes out the old 

 feather. 



