2 FEATHERS chap. 



The aid of the Palaeontologist and Geologist must thus be called 

 in to clear up many problems which present themselves to the 

 Ornithologist who does not content himself with examining exist- 

 ing forms of life alone. Archaeopteryx (p. 23) from the Jurassic 

 System is the oldest Bird known, nor are any other pre- Tertiary 

 forms recorded, save a small number from the rocks of the Creta- 

 ceous Epoch, the chief of which are the so-called Odontornithes, 

 or toothed species of America (p. 45). 



The following paragraphs on the structure of Birds will help 

 to explain the systematic account in the later chapters. 



Feathers. — Eeturning to the outward character denoted by 

 the popular saying with which we began, the Feathers ^ con- 

 stituting the pluniage may not inconveniently be first considered. 

 The general belief that they grow from almost every part of a 

 Bird's body, as do hairs in most Mammals, is erroneous ; for, 

 almost without exception, they grow in certain definite tracts 

 called pterylae, the intervening spaces, whether they be wholly 

 bare or covered with down, being termed apteria. The arrange- 

 ment of these patches is at times of considerable assistance in 

 determining a Bird's affinities ; and the subject may be studied in 

 Mtzsch's Pterylographie ^ or in a shorter form in Dr. G-adow's 

 article " Pterylosis " in Professor Newton's Dictionary of Birds. 



A feather originates thus. A conical papilla arises in the 

 derma and pushes up the epidermis, a depression forming mean- 

 while around the base ; subsequently the derma supplies a 

 nutritive pulp, while part of the epidermal layer is converted 

 into a tuft of stiff rays, . meeting and forming a short tube 

 below ; these thereafter burst their covering and protrude as the 

 rami or barbs, on which, apparently by secondary splitting, are 

 commonly produced radii or barbules. In this state we have a 

 " plumule" or "down-feather " ; but in the case of the feathers that 

 have " webs " or " vanes " (vexilla), often called contour feathers 

 (pennae or plumae), a fresh papilla forms at a deeper level, so that 

 the earlier structure is thrust forward and eventually drops off 

 from the apex of the later. Meanwhile the " dorsal " portions of 



^ The integument of a Bird consists of Skin and Feathers, the formei' beinK 

 composed of a superficial epidermis and an underlying derma or cutis which 

 is rich in sensory organs but poor in blood-vessels. The epidermis itself has 

 a horny outer layer and a softer (Malpighian) substratum. Feathers, hairs bristles 

 scales, claws and bill-sheaths are epidermal structures. 



^ A translation was edited for the Ray Society by Mr. Sclater in 1867. 



