240 MAINE AGRICULTURAL EXPERIMENT STATION. I914. 

 THE EPIDERMIS. 



A thorough study of epidermal structures, as has been stated, 

 has been made by Jeffries (4). The following statements agree 

 in the main with his observations. The outer portion of the 

 skin of the tarsal region is differentiated into two distinct 

 regions; the rete of Malphigi, and the stratum corneum or 

 horny layer. The latter, which lies outermost, consists of fusi- 

 form cells, much flattened, lying in fairly regular rows. Traces 

 of nuclear elements are visible in most specimens, but the out- 

 lines of cells are rarely discernible, for the corneum is but a 

 compact mass of cell remnants which has lost the texture of 

 living tissue. This is evidenced by its failure to take protoplas- 

 mic stains. It is this layer which is modified to form the scales. 

 As Hanau (3) has noted, the epidermis is invariably thinner 

 than the dermis ; it reaches its maximum thickness in the ante- 

 rior scales of the tarsal region. 



The cells of the rete of Malphigi may be divided into three 

 groups according to size and position, although they are of the 

 same origin, springing from the lower layer. All cells of this 

 division are held together by a homogeneous intercellular sub- 

 stance. The basement group comprises but a single layer of 

 columnar cells which are regular in form. It is from these 

 that the other rete as well as the homy layer are derived. This 

 basement stratum lies directly over and in contact with the 

 corium. Immediately above are several layers of polyhedral 

 transition cells, some cells of which project downward between 

 the upper portions of those beneath. A gradual flattening is 

 noted as these transitional cells approach the layer bordering on 

 the corneum. This last group is made up of fusiform cells still 

 more flattened, the outlines of which can be only indistinctly 

 seen. There appear to be no transitional cells between those of 

 the upper Malphigian layer and the corneum. The former 

 resemble the latter in shape but they take protoplasmic stains. 

 No blood vessels or nerves extend into the epidermis. 



THE CORIUM. 



The histology of this portion of the skin of birds has been 

 thoroughly studied by Hanau (3). Its location is directly under 

 the epidermis. Its structure is that of connective tissue, and 



