1914] Chandler: Feathers of Circus hudso)nus 361 



majority are of the postorbital type, i.e., a loosely woven, barbed 

 feather with a prolonged naked shaft. All gradations between 

 these two types are present. 



Such specially moditied bristles as these of the loral and 

 mental regions are better adapted to cover these regions than 

 ordinary contour feathers, since the latter would be more readily 

 ruffled, worn, and soiled. Possibly the bri.stles are furnished 

 with sensitive nerves at the base, as are the whiskers of a cat, 

 and function as "feelers." 



CONCLUSIONS 



In the above survey of the plumage of a single species of bird, 

 the most striking thing to come to our attention is the remark- 

 able adaptation of the form of the several types of feathers to 

 function, without involving much change in fundamental struc- 

 ture. As stated at the beginning of this paper, in such a 

 bird as Circus hudsonius there is displayed a greater variety 

 of integumentary structures, all reducible to a single fundamental 

 type, than can be found anywhere else in the vertebrate phylum, 

 and an attempt has been made in the foregoing pages to show 

 exactly what modifications of the fundamental feather structure 

 have produced the varioiis results to be observed in diverse kinds 

 of feathers to be found on the bird. I can think of no other 

 mechanism produced in nature which is so complex and yet has 

 all its parts so finely adjusted and so perfectly adapted for the 

 function it has to serve as that of a feather. In order to obtain 

 some idea of the complexity of a well-developed feather, a 

 computation was made of the number of barbules present in one 

 of the middle tail feathers of the species under consideration. 

 The figures showed that, at a very conservative estimate, there 

 are about 1,250,000 barbules present. If laid out end to end in 

 a straight line these microscopic structures, appearing to the 

 naked eye like a particle of dust, would stretch over a di.stanee 

 of more than 1000 meters. When the number of cells in each 

 barbule. which is at least twent}', and the number of feathers in 



