1883.] 205 [Jeffries. 



cells. It is this intercellular substance forming the basal walls 

 of the mucous layer which, I believe, has been mistaken for a 

 basement membrane. 



Except where organs of special sense are developed, the 

 mucous layer rests smoothly on the surface of the cutis vera, 

 no papillae occurring. The cells (pi. 4, fig. 1 c) of the mucous layer 

 vary in size in different birds, being somewhat smaller in very 

 small birds than in larger ones. In the Cormorant they measure 

 about .0075 mm. by .0125 mm., being columnar in shape. The 

 nuclei are oval or elongated parallel to the long axis of the cell 

 and measure about .006 mm. The nucleoli are quite small and 

 difficult to distinguish. In number they seem to vary from one 

 to two. 



Outside the mucous layer is a bed of polyhedral cells, b, which 

 much resemble the mucous cells in structure. As a rule, how- 

 ever, they seem to have but one nucleolus. These cells vary 

 considerably in number, according to the part, and they are 

 destined to form the outer horn-cells. 



The horn, or outer e]3idermal, cells (a) form the external coat 

 of the skin, which is thinnest on the parts protected by the plu- 

 mage. The cells are flattened, polygonal, without distinct 

 nuclei and arranged in more or less perfect layers. Nuclei 

 can be brought out by proper reagents as caustic potash and 

 the like. Like the cells below, these scurf cells are joined to- 

 gether by an intercellular substance. Desquamation shows a 

 strong tendency to occur at fixed periods, the moults, and 

 in large patches, as in frogs. This tendency is most marked 

 on the tarsus and will be considered when describing the scutae. 



Nerves and lymphatics have not been noticed in the epiderm, 

 yet both have been clearly seen in the cutis vera. I am therefore 

 inclined to doubt if many nerves enter the epiderm except in 

 parts specially endowed with sense organs. Lymphatics have been 

 well injected in the true skin yet nothing has been seen of this 

 system in the epiderm. 



The cutis vera, or true skin, though properly beyond the pro- 

 vince of this paper, is built up of fine branched connective tissue 

 filaments, with more or less connective tissue corpuscles, on the 

 outside. Deeper it is composed of fibres of considerable size 

 running in bundles in all directions. The whole is supplied with 



