1914] Chandler: Feathers of Circus hiidsonius 365 



of feathers attached to the bird's thuiiih, lint they are rednced 

 and small. Nevertheless they are very highly specialized to 

 serve a very distinct function. In the elongated lesser coverts 

 of the humerus, known as tertiaries or humerals, we have another 

 instance of a local modification supplied from the nearest and 

 most convenient source. Obviously, unless some special provision 

 were made against it, there would be an opening between the 

 spread wing and the body of the bird which would result in a 

 considerable los.s of efficiency. The humerals, which are especially 

 enlarged and modified lesser coverts, growing from a continuation 

 of the series on the humerus, serve this function, successfully 

 bridging the gap which would otherwise occur. In the increasing 

 angle of the shaft of the outer tail feathers we have again an 

 example of the extreme care taken in the fine adjustment of all 

 parts of the plumage to their particular use, since, were this 

 adjustment neglected, the tail would be in a permanently spread 

 condition, unless special muscles were developed and continually 

 used to keep the feathers closed together. 



The ordinary contour feathers of the breast and back, serving 

 for warmth and protection and to give an elastic, automatically 

 adjustable surface, do not need, and do not possess, such a highly 

 developed minute structure as do most of the wing and tail 

 feathers, but they are eminently adapted for the purpose they 

 serve. Their insertion at a wide angle with the body of the 

 bird, with a sharp bend in the shaft to bring the interlocking 

 parts of the feather to lie flat on the contour, gives a thick, 

 soft, elastic, warm covering that could hardly be more effective. 

 Where it is necessary for the feathers to lie perfectly smooth, 

 they are not inserted in this way, e.g., on the head. The strong 

 downward arch of the upper tail coverts to make them fit firmly 

 against the base of the tail feathers is also worthy of mention. 



No more perfect adaptations to function could be found than 

 the modifications of the ear coverts, eyelashes, and bristles of 

 the head. The ear coverts, by their open structure, are adapted 

 to protect the ear opening from dust and dirt, and at the same 

 time to admit sound waves without interference; the eyelashes 

 are adapted to project out over the eye and protect it as do the 

 hairy eyelashes of mammals, these feathers being made hairlikt 



