152 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
more distal in position, a single feather presents at successive levels con- 
ditions which are identical with those of a given region of a feather in 
successive stages of its growth. ‘The conditions shown in Figures 12-23 
were taken from sections marked in the diagram, Figure 1, by the num- 
bers 12-23, which are successively more and more distal in position. 
They correspond to successively older stages in the development of a 
feather germ. I begin my account of the conditions presented by the 
remiges of Sterna hirundo with a description of the conditions nearer 
the inferior umbilicus (12, Fig. 1). 
In Figure 12 (Plate 2) is shown a portion of a cross-section just above 
the umbilicus. A peripheral portion of the pulp (drm.) is shown at the 
bottom of the figure. It consists of closely packed connective-tissue cells, 
whose long axes are cut at right angles. Blood vessels are especially 
numerous at the periphery of the pulp. 
Between the pulp and the epidermis lies the so-called basal mem- 
brane. This is seen most favorably in preparations where decolorization 
was not carried very far. I have also recognized this structure in picro- 
sulphuric material, but far less clearly. Studer (’73) described as 
structureless a membrane lying between the dermis and epidermis of 
the feather, but later (78, p. 425) noticed that it was cellular. Davies 
(89) noted Studer’s observations of a basal membrane in his review of | 
Studer’s work, but, in his own account, does not mention the basal 
membrane as a separate structure. He treats of it as a part of the 
connective-tissue pulp, without, however, discussing the subject. 
That this structure is cellular in Sterna hirundo, is evident from the 
presence of the nuclei which are inclosed in it (Plate 2, Fig. 14, nl.). 
There can be no doubt, moreover, that it is of dermal origin, for the 
nuclei have the characteristic smaller size of dermal nuclei; besides, a 
sharper line of demarcation exists between the membrane and the cylin- 
der-cell layer than between it and the dermal cells. The nuclei are not 
abundant, but where they do occur they leave no doubt as to the cellu- 
lar nature of the structure. 
Proceeding distally along the fundament of the feather, the basal 
membrane becomes thinner and therefore less conspicuous (Figs. 
15-21). 
The epidermis of the feather germ, including the feather sheath, 
comprises four fairly well marked layers: The deepest layer, that next 
the pulp, consists of a single row of spindle-shaped cells (cl. cyl.) elon- 
gated in the direction of the radii of the cylindrical germ, and called 
cylinder cells. Except for their blunt deep ends and their weaker stain- 
— ee 
a 
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