380 Fatio on the Forms and Colours of Plumage. 



noticeable at the base of a growing feather. A feather once 

 dried, receives no more blood or pigment, because it no longer 

 grows from its base." 



Besides variations of colour produced by moults, other colour 

 changes occur in most birds, taking place gradually from the 

 end of the autumn, and in some cases going on rapidly at the 

 approach of spring. Two principal phenomena are exhibited 

 in these colour changes : " the interior pigment dissolves and 

 spreads, while the extreme parts of each feather fall and allow 

 the new colouration to appear, which has been formed below 

 them, and thus showing suddenly a new livery which had 

 been concealed." 



M. Fatio describes the latent colour as residing in pig- 

 mentary granules, not dissolved, isolated, or grouped, and 

 usually confined to the centres of the different parts of the 

 feather to which they are to impart a new colouration. The 

 colour which is seen is spread through the cortical substance of 

 the same parts, and arises from an anterior colouration of other 

 pigment granules, or of a subsequent solution of latent 

 pigment deposits. Light, atmospheric moisture, and tem- 

 perature are agents influencing these changes, operating in 

 conjunction with food and the sanitary conditions of the bird. 



ce Here," exclaims M. Fatio, " are two feathers from the 

 same part of the same bird — one an autumn feather, uniform, or 

 variegated, with clear tints, dark, but comparatively feeble 

 and not lustrous; the other, a spring feather with more 

 definite and brilliant colouring. I place the autumn feather 

 under the miscroscope, and, studying it with magnifications of 

 from 80 to 300, I notice in its tissues the two conditions just 

 spoken of; the colouration more or less strong, transparent, 

 and diffused : and also its internal deposits somewhat diminished, 

 or disappeared, from the extreme parts, such as those of the 

 barbs and barbules. The pigment in the axis has been dis- 

 solved in, and spread abundantly through, the surrounding 

 cortical substance; some parts being largely developed in 

 their proportions." 



After citing the opinions of other observers, M. Fatio 

 describes his own experiments, and states that by exposing the 

 feathers of the starling and linnet to the influence of moisture 

 by immersing some in water, and floating others on the surface, 

 they soon exhibited a sensible development of their cortical 

 substance in the barbules of the starling, and in the barbs of 

 the linnet. At the end of twenty days the pigment was not 

 dissolved, or only so imperceptibly. 



In another experiment M. Fatio moistened feathers with 

 water, and gradually heated them on a plate of glass. He 

 noticed at first a slight extension of colour in the tissues, and 



