STRONG: DEVELOPMENT OF COLOR IN DEFINITIVE FEATHER. 185 
EXPLANATION OF PLATES. 
. 
Figures 12-21 and 23 are from sections of a feather germ (secondary) of Sterna 
hirundo which was fixed with Hermann’s fiuid and stained in iron haematoxylin. 
They represent corresponding regions, indicated in Figure 2 by an asterisk (*), — 
but taken at different levels. The levels of the sections are indicated in Figure 1 
by the horizontal lines 12, 13, 14, ete. Figures 3, 35, 36, and 37 are also from 
maierial fixed in Hermann’s fluid and stained with iron haematoxylin. Figures 
22, 24, 38, 39, 40, 41, 42 were made from material fixed with Kleimenberg’s picro- 
sulphuric mixture and stained in Kleinenberg’s haematoxylin followed by eosin. 
All drawings were made with the aid of a camera lucida. 
arm. 
ABBREVIATIONS. 
Barb. dst. 
Barbicel. eth. 
Barbule. Jud. 
Calamus. gran. pig 
Cylinder-cell layer. ham. 
Intermediate cells. la. ar. 
Medullary cells. mac pig. 
Pigment cells. marg. - 
Inner sheath cells. 
Column of cells forming a mb. ba. 
single barbule. med. 
Red blood corpuscles. ni. 
Ridge of epithelium marked nil. 
off by mb. ba. pre. 
Ventral ridge of barb. pre. 
Irregular ridges of epithe- rch. 
hum. ser. cl. 
Cortex. 
Cytoplasm. tu. 
Dorsal. umb. inf. 
Derma. z. 
Distal. 
Epithelium. 
Fundament. 
Pigment granule. 
Hamuli or hooklets. 
Axial plate. 
Pigment patches. 
Recurved margin of prox- 
imal] barbule. 
Basal membrane. 
Medauila. 
Nuclens. 
Nacleolas. 
Process of pigment cell. 
Proximal. 
Rhachis. 
Row of barbule cells seen 
in transvrerse section. 
Feather sheath. 
Inferior umbilicus. 
Ventral. 
