72 INTRODUCTION. 



the median groove of the shaft, over which lies a small laminar 

 prolongation of the tnbe. This arrangement is what is ob- 

 served in qnill-feathers in general ; but in most ordinary 

 feathers there is no vacuity behind, and the internal membrane 

 makes its exit undivided at the commencement of the gTOOve. 

 The shaft is distinguished from the tube by its being opaque, 

 which is caused by the internal corky substance, the external 

 horny coat being of the same nature as the tube, only attenu- 

 ated, and more so, as has been said, on the back, than on the 

 fj\ce or sides of the shaft. 



o. The wehs, of which there are two. Fig. 17, c, d, one on 

 either side of the shaft. The web is a lateral prolongation of 

 the external layer of the coat of the shaft, into a series of fila- 

 mentous substances, ordinarily placed in apposition, and by 

 their association in this manner forming a stiffish elastic ex- 

 pansion. The filaments of which the web consists are named 

 barbs. 



The barb, Fig. 18, a, b, c, is a very thin 

 linear membrane, being an attenuated 

 continuation of the outer pellicle of the 

 shaft, and arising from it at the angle 

 Fig. 18. Barbs. Barbiih: formed by the meeting of the dorsal 

 and lateral surfaces, along the edge of the latter. The 

 direction of the barbs is obliquely outwards with respect 

 to the shaft, that is, inclining more or less at an acute angle 

 toward the tip of the shaft. Each barb is flattened or com- 

 pressed vertically with reference to the shaft, considering it 

 horizontal with its face downwards, concave on the side next 

 the tip, convex on the other, so as to fit to its neighbour on 

 either side. It terminates at its lower part, or that on the 

 concave surface of the feather, in a sharp edge, generally dia- 

 phanous, which is reflected in the direction of the tip of the 

 feather. The body or substance of the barb is pretty uniform 

 in thickness, and it is only when viewed in connection with 

 the barbules that it could with any propriety be said to be 

 triangular. 



From the upper part or edge of each barb there proceed two 

 sets, one on either side, of minute filaments, having a direction. 



