INTRODUCTION. 3 



parents (Altrices), and so are many of those which are born down-clad, but a great 

 number of the latter are able to run about immediately upon leaving the egg (Pra> 

 coces). A few birds remain so long within the egg that the feathers are developed 

 before the shell bursts, this being the case with the young talegallas, and these might 

 be called Pteropsedes. 



As remarked above, the feather is formed on a dermal papilla. At an early stage 

 such papillae arise above the surface of the skin, each of which is grooved longitudi- 

 nally on one side. This median groove sends off laterally numerous smaller ones in 

 an obliquely upward direction, gradually becoming shallower. The secretion of the 

 papilla moulds in these furrows, and, when pushed upward by new formations below, 

 dries and splits into a feather, consisting of a scape and disconnected lateral barbs. 

 These imperfect feathers are called plumules, and, taken collectively, constitute the 

 down. While the papilla from which these plumules were formed sinks later on into 

 a pit or follicle of the skin, another crop of more perfect feathers starts from papilla? 

 at the bottom of pits which are situated at the intersections of numerous ridges 

 of the skin (the latter without sudoriferous glands and sebaceous follicles). These 

 papillae are more deeply grooved, and have, moreover, A T ery often a corresponding but 

 slighter furrow on the opposite side, from which originates a usually small extra feather, 

 known as the after-shaft (hyporachis), and attached to the under side of the main 

 shaft. These stronger and more perfect feathers, which are called contour feathers, 

 consist of a central stem and a lateral ' web ' on each side. The former is composed 

 of two parts ; a lower, cylindrical, and hollow portion, the quill proper, enclosing the 

 papilla, which shrivels when the feather ceases to grow; it merges into the terminal 

 part, the shaft, which is four-sided and solid, and from which spring two lateral sets 

 of barbs or radii ; these have on their margins secondary processes, barbules, which by 

 means of small hooks or barbicels interlock with the neighboring barbs, thus unitin" 1 



o o ' o 



them into continuous and elastic 'webs,' termed the inner or outer web, according to 

 the relative position to the median line of the body. 



Only in a few of the recent birds, as in penguins and ostriches, are the feathers dis- 

 tributed evenly over the whole body. In all Euornithes they are arranged in special 

 and regular groups or tracts (pterylae), separated by naked or downy spaces (apteria), 

 which are concealed by the overlying feathers of the neighboring tracts, an arrangement 

 by which smoothness of the plumage is secured whatever movement the bird may under- 

 take. It may be regarded as a rule that the smaller the feathers in a tract the smaller 

 are the separating spaces, the latter sometimes becoming so narrow as to be nearly 

 obliterated. The different grouping of the tracts, their distribution and ramification, 

 are subject to considerable variation, and are to a certain extent valuable for syste- 

 matic purposes, because sometimes diagnostic of important divisions. 



Two of the pterylas are of special interest and importance the alar and the 

 caudal tracts, both including the strongest feathers of the whole body. From the 

 former spring the remiges, which form the essential part of the wing, and without 

 which no bird can fly. Those which are fixed to the hand are called primaries ; 

 secondaries are those on the forearm, the three innermost of which are styled tertiaries. 

 The number of primaries is usually ten, often nine, very seldom eleven ; that of sec- 

 ondaries from six to forty. The bases of these are overlaid by several rows of larger 

 and smaller contour feathers, the upper or under wing coverts, according to their posi- 

 tion on the upper or lover surface of the wing. For further detail we refer to the 

 accompanying cut, which will give more information at a glance than we can detail in 



