Jeffries.] 218 [February 7, 



so well known that they may be passed over. I would only call 

 attention to the fact that feathers may grow from the edge or 

 beneath the scutae, as shown by certain breeds of hens. (Figs. 

 18, 19, 21.) In such cases the feathers are set in regular pockets, 

 as in the rest of the body. 



Though all the general works on comparative anatomy have 

 more or less to say about the structure of the scutae, I know of 

 but two papers which enter into detail. Herbert (4) gives two 

 figures of the histology of the scutae, and figures certain branched 

 papillae which he says extend from the cutis vera between the 

 cells of the epiderm. The other work, that of Hanau, I have not 

 been able to procure, nor even to find any summary of it. 



An adult scuta has but three different layers of the epiderm. 

 (Fig. 22.) These are the mucous layer, the transitional cells and 

 the horn cells. The mucous layer rests evenly on the corium 

 without the intervention of such papillae as occur in the toe-pads, 

 which will be described later. The cells vary more or less in size 

 in different species of birds, and in different parts of the scuta. 

 At the edge of the scuta, where the mucous layer of the outer 

 and inner surfaces nearly meet, the cells are apt to be cuboidal ; 

 higher up, above the flap, they are columnar, as a rule. The nuclei 

 are of good size, roundish and often with two or more nucleoli. 

 The cell walls are difficult to stain, but owing to their different 

 density show up as irregular lines. It is these cell walls, which 

 assume all sorts of branching appearances, that, I believe, repre- 

 sent the papillae of Kerbert. At all events, no papillae are to be 

 seen in very thin sections, while the cell walls and intercellular sub- 

 stance are quite distinct. Here it is of interest to note that these 

 supposed papillae will not stain with the same reagents that 

 stain the true filaments in the tongue and papillae of the toe- 

 pads. 



The transitional cells near the mucous layer are much like the 

 mucous cells. The outer ones, however, are distinctly fusiform 1 

 in shape, and have their nuclei correspondingly elongated. These 



1 There are two classes of horn-cells: those forming the outer coat of the epiderm 

 in general and those forming claws and the like. The first owe their name to the 

 toughness of their walls and lack of active protoplasm and are of variable shape. 

 Horn-cells, properly speaking, are fusiform, very solid, and have wrinkled walls; they 

 oco'.i ir- «.ll hard appendages. 



