140 PTERYLOGRAPHY. 



rows of contour-feathers in the tracts is the rule not only in the case of every tract, whether 

 broad or narrow, in this family, but also in all other birds, and occurs equally in the 

 Aerial, Terrestrial, and Wading Birds, but cannot always be recognised with equal distinct- 

 ness in all these on account of the narrowness of the tracts. Essentially the natural direc- 

 tion of these rows appears to be from within and in front, outward and backward, so that the 

 angle formed by each pair of rows at their point of contact in the median line opens pos- 

 teriorly ; but as this contact is always deficient on the ventral surface, and is only distinct on 

 the dorsal surface when the dorsal tract contains no longitudinal space, the rows of feathers not 

 only appear to run in an opposite direction in many places, but two rows may even seern to meet 

 and intersect each other, forming acute angles with their obtuse complementary angles of 

 course because the distance of each two feathers in each row being the same, these mutually cor- 

 responding feathers themselves again form rows. These rows may be very distinctly recognised 

 on birds plucked quite clean, by the follicles in which the feathers are inserted, and the small 

 cutaneous muscles which pass from the interior lower extremity of each contour-feather towards 

 all the four neighbouring feathers, and are inserted on the inner surface of the skin in the circum- 

 ference of the follicle in which the feather is inserted. These feather-muscles, which are employed 

 in the erection and depression of the contour- feathers (see p. 13), are seen most distinctly, on 

 account of their size, in the Natatores, and especially in those with a pneumatic skin, such 

 as Dysporus and Pelecanus. But no one can overlook them even in our Domestic Goose, when 

 the inferior tracts of this bird, beautifully cleaned, are brought to table with the smoked 

 breast. The regular serial position of the contour-feathers is so distinctly expressed as to 

 be unmistakeable. 



Between each four feathers, which together form a rhombus, there is always at least one 

 down-feather, and this is exactly in the middle of the space just indicated ; but besides these 

 we not unfrequently find others which appear to be intruded between each two contour-feathers 

 of each row, so that in such a case the rows consist of alternate contour- and down-feathers ; 

 or they are seated upon the surface of each individual rhombus, but still in the same direction 

 with regard to the contour-feathers. These down-feathers are then always smaller than those 

 which occupy the middle of the rhombic spaces ; but neither of these positions can be recognised 

 after the down has been pulled out, partly because the down-feathers have much smaller tubes, 

 but partly because they are entirely destitute of the above-mentioned feather-muscles. The 

 difference between the down-feathers is, however, usually a comparative one, those occupying the 

 middle being larger than those between the contour-feathers ; nevertheless in Anas pcnelope I 

 have found the larger down-feathers to be of a darker colour than the smaller ones. Of course, 

 this difference must disappear when all the down-feathers are white, as in the white Domestic 

 Goose, Swans, or other white Swimming-birds ; but in those with varied colours the down-feathers 

 are, as usual, grey. As regards the spaces of the Natatores, these likewise have a dense downy 

 covering, which perhaps also consists of double down-feathers. I need scarcely remark, as it has 

 already been stated in the first section, that each contour-feather has its filoplumes about it, and 

 that there may be as many as ten in this group, e. ff. in the Geese. In such cases, although 

 they have a similar structure, they are of very various lengths. 



The very frequent, although not universal deficiency of the after-shaft on the contour- 

 and down-feathers appears to arise from this closely approximated position of the feathers, which, 

 without it, form a very dense and securely protective covering; for it is exactly in those Swimming- 



