Jeffries.] 220 [February 7, 



description given by him will be followed in this paper. Scutae 

 occur on the tarsus and dorsal aspect of the foot, and are dis- 

 tributed and modified in ways well known to systematic ornith- 

 ologists, hence they need not be considered here. We must, 

 however, bear in mind that feathers as well as scutae occur on the 

 tarsus and even on the toes, so that we may not mistake the one 

 for the other in studying sections. 



The first signs of scutae appear at or about the tenth day as 

 little ridges or folds of the skin, and are thus distinguished from 

 the feathers, which are true papillae. Kerbert 1 describes their 

 appearance in the following words : "Die durch Wucherung der 

 Cutis entstandene Papille wachst nun noch eine Zeit lang radiar- 

 symmetrisch weiter, so dass sie von der Anlage der Embryon- 

 aldune gar nicht zu unterscheiden ist." This is a mistake due 

 to describing longitudinal sections of the tarsus and disregarding 

 surface views ; the appearance of longitudinal sections of down 

 papillae and scutae are the same. 



Until the appearance of the scutae the skin on the tarsus and 

 toes follows the general rule of development and consists of the 

 " epitrichial " layer, the basement mucous cells and about one 

 layer of cells between. The epitrichial cells are as yet much like 

 the other cells of the epiderm and do not form a compact layer 

 of hexagonal cells. They are simply rather flattened cells, with 

 nucleus and nucleolus, of a roundish form when seen from above. 

 Accordingly there are considerable spaces between the cells that 

 are filled up with some sort of intercellular substance. The 

 mucous layer is built up of a layer of cells varying from cuboidal 

 to columnar in form packed close together. The cell walls are 

 thick on the inner surface, that is the side next the derm, and 

 form a sort of membrane. The walls between the cells are thick- 

 est near the base of the cells and thin down towards the outer 

 end. The cells between the epitrichial and mucous layer are 

 polyhedral and packed quite close together. Both the mucous 

 cells and those outside are full of protoplasm, and provided with 

 large nuclei for the most part oval in form, though some seem 

 cuboidal. The mucous nuclei contain as a rule two nucleoli, one 

 nearer the base of the cell than the other, sometimes one or 



ilbid., p. 40. 



