10 PTERYLOGRAPHY. 



3. The BARBS (Plate I, fig. 1, c) issue in rows on both sides of the main shaft, and also of 

 the aftershaft when the latter is present ; they form, with the parts seated upon them, the so-called 

 VANE (vexillum, Fahne). They are usually compressed lamellae of lanceolate form, which are 

 seated on the shaft in such a manner, that one of the two edges is directed upwards and out- 

 wards, and the other downwards and inwards towards the body of the bird. These barbs 

 attain their greatest depth in the outer half of the vane of the remiges ; in other respects 

 they exhibit very great diversities in different birds as regards their form, length, and thickness. 



4. The BARBULES (Plate I, fig. 3, b, c), are similarly emitted in two rows from the upper 

 margin of the barbs, anteriorly towards the apex and posteriorly towards the base of the 

 feather. But it must be noted, that barbules spring from the apex of both the mainshaft and the 

 aftershaft where the formation of barbs ceases, and that they sometimes occur even in the interspaces 

 of the barbs 1 when the latter stand wide apart. In this case they are extremely similar to those 

 of the barbs, and must, therefore, be indicated by the same term. The barbules, which might 

 be compared to the leaves of a tree, just as the stem to its trunk, are much more numerous than 

 the barbs, and are distinguished among the constituent parts of the feather by the great variety 

 which they present in form, length, and delicacy. Commonly, however, their base is compressed, 

 and their superior extremity somewhat filiform. Moreover, the anterior row of barbules on each 

 barb, or that which is directed towards the apex of the feather, is very frequently distinguished 

 from the posterior series, not only by the form, but also by the parts which in turn issue from 

 the barbules. 



5. The BARBICELS (Plate I, fig. 4, #), when they occur, are the most numerous of all the 

 parts of feathers, and originate, like the hooklets, almost solely from the barbules of the anterior 

 series. They form, as it were, their branches, and are simple, filiform, straight, or nearly so, 

 and stand either in a single or double series. They never occur on the lower part of the 

 barbule (unless we are to regard the broader lobes (fig. 4, c), which are sometimes met with there 

 as representing them), and even on the upper part they are not always present ; in this case, 

 however, they are entirely wanting. When the barbules are downy in form, small knots, 

 alternating with thin interspaces, appear to take the place of the barbicels, especially if the knots, 

 as is not unfrequently the case, are produced into opposite points, and thus represent barbicels 

 (figs. 9, 20, and 23). 



6. The HOOKLETS (Plate I, fig. 4, b), like the barbicels, are only perceptible under the 

 microscope, and likewise constitute lateral processes of the barbules, but they only occur on the 

 anterior series of the latter, never on the posterior, and also only on one side of each barbule, 

 namely, the lower side. They appear to differ from the barbicels only by their hooked curvature 

 and their peculiar purpose. The hooklets of the anterior series of barbules of each barb interlock 

 with the posterior series of barbules of that which immediately follows it (see Plate I, fig. 2), 

 in such a manner that each booklet of one barbule lays hold of a barbule of the next barb, and 



This is the case, for example, iu the feather represented in fig. 1 at the part of the shaft where 

 the barbs of the basal half stand somewhat wider apart. With regard to the remarkable structure of 

 this part see the explanation of figure 6. 



