238 



NATURAL HISTORY. 



The interstices between the barbs are filled up by the barbules, pointed processes, which stand in the 

 same relation to the barbs as the barbs do to the rachis. The barbules themselves may be laterally 

 serrated and terminated by little hooks, which interlock with the hooks of the opposed barbules. In 

 very many birds each quill bears two vexilla ; the second, called the after -shaft (6) (hyporachis), being 

 attached on the under side of the first,"* close to the junction of the shaft with the quills. 



In all the feathers of the Ratitse, and in the case of all but the contour feathers in other birds, 

 there are no barbules to the barbs. The pennse are ordinarily arranged in definite patches, or areas on 

 the bird, and the shape and size of these, and their relation to one another, differ in many birds. 



The qftershaft (b) is ordinarily a smaller vexillum, which is attached to the under side of the larger 

 one at about the point where the rounded quill passes into the stem. 



It is not necessary to notice these important characteristic structures more fully now, as they 

 will have to be considered in explaining the distinctions between the great groups of birds, and we pass 

 on to notice that the same kinds of birds are not found everywhere, but that they have, as groups, a 

 remarkable geographical distribution. 



In the following pages the distribution of birds is often alluded to, although it will naturally be 

 impossible to discuss, within these limits, all the various phases of the study which the geographical 



distribution of the feathered tribes opens up to us. At the 

 same time sufficient evidence will be given to show that 

 birds are not scattered without order over the earth, but are 

 more or less restricted to certain spots. 



The six natural history or distributional provinces into 

 which the world is ordinarily divided by modern naturalists 

 were determined, first of all, from the study of the birds ; 

 and in fixing the boundaries of each division the wading 

 birds and many swimming birds must be left out of the 

 question, as they are creatures of such very extensive flight, 

 and wander almost from pole to pole. A natural region, 

 therefore, can be marked only by its resident forms of bird 

 life, or at the most by the birds which breed within its 

 limits; and the six regions alluded to provide us with many 

 excellent reasons for believing that they possess well-defined 

 physical boundaries. No Capercailzie, for instance, was ever 

 found out of the Palcearctic^ region, which comprises 

 Europe and the greater part of Asia above the line of the 

 Himalayas and the Yangtze-kiang River in China. This 

 region is also characterised by a large number of Buntings, 

 Warblers, Grouse, &c. In the Nearctic\ region there is 

 a certain similarity to the European and Siberian Avifauna, 

 Grouse, Ptarmigan, Wax wings, Magpies, Ravens, &c., 

 being commonly found throughout the two regions. North 



America possesses, however, several forms peculiar to itself, though it is by no means so rich in 

 species as is the Neotropical^ region, which commences south of a line drawn through Northern 

 Mexico, and includes the whole of Central and Southern America. Within this large area are contained 

 whole families of birds, such as Toucans, Mot-mote, the vast majority of the Humming-birds, Trogons^ 

 besides innumerable genera of Tanagers and other forms, so that this region is by far the richest in the 

 world as regards bird life. The Ethiopian region embi'aces all Africa below the Sahara Desert and 

 Madagascar : Plaintain-eaters, &c., are characteristic of this region. The Indian region skirts the 

 Palsearctic, and includes the remainder of Asia below the Himalayas and the Yangtze-kiang ; the 

 Malayan Peninsula, the Sunda Islands, and the Philippines, belong to this region, which contains all the 



* Huxley, "Anatomy of Vertebrates," p. 274. 



f TroAatds, old ; ap/cros, north : i.e., the northern division of the Old "World. 

 J ve'os, new ; apxros, north : i.e., the northern division of the New World. 

 vios, new ; Tponx/cds, tropical : i.e., the tropical division of the New World. 



PARTS OF A FEATHER. (After Nitzsch.) 



