1883.] 219 [Jeffries. 



cells are simply getting ready to be converted into cells like those 

 of the outer horn-coat. In form they resemble the horn-cells, 

 but differ in that they are protoplasmic and stain deeply with 

 picrocarmine. 



The horn layer is sharply marked off from the transitional cells ; 

 no cells existing, as in embryos, which are half horny in texture. 

 The cells are fusiform, dense and very compact. Specimens 

 hardened in alcohol show the cell walls well ; the nuclei can often 

 be brought out by eosin in benzole. The cells may be softened 

 and separated by a 33 % solution of caustic potash. 



Pigment is to be found in the epiderm, in the mucous and 

 adjacent cells, in many species of birds. The pigment is of an 

 oily nature and simply diffused through the cells. Another class 

 of pigment, namely, a dark pigment in cells, like that described 

 when speaking of the skin proper, is to be found under the epi- 

 derm in dark-legged birds. 



In speaking of the skin the tendancy to moult the outer cells 

 in mass was referred to. The same thing, only more marked, is 

 to be seen in the scutae. The whole of the outer layer of horn- 

 cells is shed in pieces of about the size of the scatae. I have ob- 

 served this process in canary birds, and have studied sections 

 taken from a pigeon in the act of moulting the horn layer. In 

 this case the outer coat of horn split off very easily, but could 

 be kept on by careful manipulation. Beneath the layer, which 

 was splitting off, was another layer of the same nature and thick- 

 ness but firmly attached to the deeper layer. The transitional 

 cells were fusiform, but not so numerous as is often the case. 



The centre of a scuta is formed by a fold of the cutis vera 

 composed of rather compact connective tissue. Just below the 

 mucous layer there are often to be found well developed, abundant 

 capillary and lymphatic systems. Nerves seem to be very scarce, 

 but I have not employed special reagents to bring them out. 

 That there is little sense of touch in this region can easily be 

 proved by the difficulty of arousing caged birds by pricking the 

 tarsus, as compared with the toe-pads or soft parts of the head. 



DEVELOPMENT OF SCUTAE. 



The development of the scutae, or scales, on the tarsi of birds 

 1 as been studied by Kerbert (4) in the chick. Accordingly the 



