378 Fatio on the Forms and Colours of Plumage. 



still more so the barbules in different groups of birds, or in 

 different positions of growth. Down is often coloured : some- 

 times by the irregular diffusion of an internal pigment, in 

 its barbs and barbules, and sometimes by pigment deposits in 

 regular order and definite positions, and in parts swollen out, 

 like the antennas of certain insects. 



" After a greater or less lapse of time the feather, which has 

 followed the path prepared for it by the cutaneous down, drives 

 before it the latter and its sheath, and at last thrusts out its 

 downy termination. The great quill feathers, whether wing or 

 tail, generally appear first, and a feather generally con- 

 sists of a stem, or central axis ; barbs, or secondary 

 •axes, lateral or branching from the former ; barbules, 

 tertiary axes implanted in the barbs, or between them on the 

 stem ; hooMets [crochets), appendages of the barbules, or 

 quaternary axes.'" These parts exhibit an epidermis, formed of 

 flat, irregular cells, and below this a larger cortical substance, 

 formed of elongated cells, or their fibres ; and in the centre a 

 medidlary axis, continuous or segmented, formed of regular 

 pigment cells, polygonal or rounded. Besides down and 

 feathers, most birds have, on the nostrils or feet, piliform 

 feathers, which, as their name intimates, resemble the hair of 

 animals. They are stems without barbs. Some birds, like the 

 wax-wing (Bombycilla gamda), have horny and coloured 

 developments afc the end of some of their feathers, which, as 

 we shall show, are probably barbs conglomerated together. 

 Other species have defensive spines composed by the union of 

 several feathers, united by extravasated pigmentary matter, and 

 strongly reminding us of the formation of rhinoceros horn, 

 by the coalescence of hair. 



In studying feathers, M. Fatio says we must distinguish 

 in the hooklets between those which have true quaternary axes 

 and those which are merely outlying portions of the cortical 

 matter. The first feather of a young bird is not always 

 constructed exactly like that which succeeds it. Its barbs are 

 lower and more distant, and its barbules have fewer hooklets. 



In a young bird still in its shell, Engel has shown the 

 existence of definite spots and rows of mother cells from which 

 the feathers arise. " The primary cell divides into smaller cells, 

 some of which accumulate in a basilar bulb, and then range them- 

 selves round the circumference, and others occupy the centre. 

 The sheath which envelopes these primary materials, has at its 

 base an orifice, commonly called the inferior umbilicus, and 

 through it pass blood vessels, which convey to all parts the 

 elements necessary for their progressive development. The 

 plastic pigment-bearing matter forms gradually, and the cells 

 which it produces, and as they take up their places they elongate 



