360 CLASS xvr. 



without any provision for feeling being observable. In some birds 

 the bill may serve as an organ of touch, as in the ducks, where 

 the skin that covers it is thin and soft and has many branches of 

 the fifth pair of nerves distributed to it. 



We may here touch upon the feathers of birds, a covering of 

 the skin which is peculiar to this class, and to which the body of 

 these animals is indebted not only for the ornament of beautiful 

 colours but also for the graceful rotundity of form by which it is 

 distinguished. The feathers have, at their inferior extremity, a 

 shorter or longer horny tube, the quill (scapus, calamus), by which 

 they are attached to the skin. In the part which extends onwards 

 towards the point, named the shaft (rachis) there is on the outer 

 surface, which is smooth and somewhat convex, a lamina that is 

 produced from the horny basal piece, and extends to the extremity 

 of the feather, becoming gradually narrower. On the inner surface 

 the shaft has a longitudinal groove. The shaft consists of a white 

 spongy substance, resembling the pith of an elder-branch, which 

 arises in the tube of the shaft by two or three roots. The quill, 

 again, is not entirely hollow but contains some membranous parts 

 or partitions (the so-named pith of the feather) , which are fixed to 

 the lower and the upper ends of the quill when the pith of the shaft 

 begins to be formed, and are received within one another like 

 funnels. From the shaft proceed obliquely on each side towards 

 the point of the feather branches (rami NiTZSCH, radii or barbce of 

 other writers). This branch-like part of the feather is named flag 

 (vexillum) or vane. The horny laminae of which it is composed 

 are also provided on each side with finer rays (radii NITZSCH, bar- 

 bulce) scarcely visible by the naked eye; the anterior row of these 

 rays, i. e. that which is turned towards the point of the shaft, sup- 

 ports minute microscopic hairs, which, in part, are bent into hooks 

 at their extremity and cross the posterior rays of the branch im- 

 mediately preceding. It is by these booklets that the branches of 

 the vane, especially in the flag- and tail-feathers so completely 

 interlock; when the attempt is made to separate them, they seem 

 to stick together 1 . In the feathers of very many birds there issues 



1 A good figure of this arrangement maybe found in HOOKE Micrographia, Tab. 23, 

 fig. 2 ; the figure of PERRAULT, on the contrary, given by OWEN in TODD'S Cyclop. I. 

 P- 35> does not correspond with nature. 



