ARRANGEMENT OF FEATHERS. 11 



pany each contour-feather. Down-feathers occur on any or all parts of the 

 body. Generally they are either confined to areas free from contour-feathers, 

 or wanting these and mixed with the contour-feathers, but in many water 

 birds a dense coat of down completely covers the body. Among contour- 

 feathers, down-feathers are arranged frequently in a quincunx in the space 

 marked out liy four contour-feathers, tiemipluineii occur associated with the 

 contour-feathers, generally, but are often mixed with down. They may be 

 found on any part of the body. 



The contour -feathera rarely occur uniformly scattered over the body. 

 Such an arrangement, however, is found in the Penguins. Among the 

 Ostriches and their allies, the feathers, though not true contour-feathers, are 

 uniformly distributed over the body in the adult. In the Ostriches, however, 

 the young bird has the feathers confined to definite spaces, so that in that case 

 the uniform covering would seem not to be the primitive condition. In nearly 

 all other birds, contour-feathers occur only on definitely limited portions of 

 the body, which are therefore called the feather tracts ov jAerylae; the spaces 

 between the tracts, which are free from contour-feathers, are called apteria. 

 Besides the tracts which cross the head, and those which include the wings and 

 tail, the principal tracts are as follows: the upper cervical tract, the dorsal, 

 the humeral, the femoral, the tibial, the lower cervical, the sternals, and the 

 ventrals. Rarely, we find instead of upper and lower cervicals, two lateral 

 cervicals. Any of these tracts may be wanting, but the positions of those pre- 

 sent are suflSciently indicated by their names. In size, width, form and 

 density, there is the greatest possible variety, birds of different orders show- 

 ing marked differences in all these matters. For this reason, the arrangement 

 of the tracts is a matter of great importance in classification, and is technically 

 known as the pteri/los is of the bird and the stud}^ of pterylosis is called ^^^e^-y- 

 lography. By many writers it has been assumed that the pterylosis is deter- 

 mined by the habits and body-form of the bird, and is consequently an adap- 

 tive and easily modified character, but there is much evidence to the contrary, 

 and it is entirely possible that the fundamental plan of the pterylosis is one of 

 the most deep-seated and least modifiable of the morphological characters of 

 birds. It must be admitted that our knowledge of the pterylography of birds 

 is far too imperfect for us to make positive statements as to the value of 

 characters furnished by pterylosis. 



The largest feathers are generally borne on the posterior ends of the 

 tracts, and this is especially true of those which include the wings and tail. 

 In these tracts are included those feathers which are of such importance to the 

 bird in flight, the remiges (rowing-feathers) and the rectrices (steering-feathers), 

 together with their coverts. The reiniges are borne on the posterior upper- 

 side of the hand and arm, and are grouped under 3 heads, according to their 



