TEGUMENTAUY SYSTEM. 67 



called, in accordance with their form and function, either cilia or 

 hamuli. The former, where they occur, as in the feathers of the 

 Goose, are the most numerous of all the parts of the feather, and 

 proceed with the hooklets only from the foremost series of barbs ; 

 they are situated only upon the upper edge of the barb, and stand 

 either in a double or only a single row. In the barbs of downy 

 feathers small nodules appear to supply the place of the cilia. The 

 cilia, like the hooklets, can only be seen with a magnifying power. 

 The hooklets form likewise lateral processes of the barbs, but are 

 found only upon their anterior series and upon the inferior side of 

 each barb. They differ from the cilia by the hook-shaped curve of 

 their extremities, the hooklets of an anterior series of barbs catching 

 upon those of the one behind it, so that in this way the barbs are 

 held fast. This arrangement is of importance for the flight of the 

 bird, as by means of it the barbs of the feather are prevented from 

 being torn asunder by the air, which would necessarily injure the 

 power of flight. 



The Contour-feathers are, as a rule, formed in the manner above 

 stated, and have a perfectly-formed and stiff shaft. Their structure 

 is most complete in the primaries of the wing, and the remigial feath- 

 ers of the tail. The cilia and hooklets, however, are occasionally 

 wanting, as in the Ostrich and Nandou (Rhea) ; and in other birds, 

 as in the Cassowary, the barbs are absent. At the extremity of the 

 bristles at the angle of the mouth, and upon the chin, and the 

 eyelashes, the barbs are also wanting, or there is found only a 

 membranous projection in place of a vane. The remarkably long 

 spurs of the wing in the Indian Cassowary are shafts without any 

 barbs. 



The J) own- feathers pass occasionally into quill-feathers ; although 

 they mostly lie concealed, yet they frequently form large freely ex- 

 posed masses, as upon the neck of many of the Vultures. A down- 

 feather frequently stands in the middle between four quill-feathers, 

 and forms with them a quincunctial figure. The true down feath- 

 ers exhibit an articulated structure, and appear like so many cones 

 inserted in each other, and exhibit under the microscope, when they 

 are of a gray color, a particolored appearance like that of the gray 

 hairs of the Mouse, &c. The broader nodules are black, the inter- 

 vals between them transparent and colorless. The down-feathers of 

 nestling and young birds have very delicate barbs, and none, or only 

 very small, nodose dilatations. 



The Plume-feathers (filo-pluma3) differ very strikingly from the 



