STRONG: DEVELOPMENT OF COLOR IN DEFINITIVE FEATHER. 165 
epidermis only, or (3) in both. Most writers who advocate origin from 
the blood have described pigment as being formed in the dermis, either 
in ordinary connective-tissue cells, or in special cells differentiated for 
the purpose, which in the case of epidermal pigmentation wandered 
from the dermis into the epidermis or sent amceboid processes up be- 
tween the cells of the cylinder-cell layer. 
I have found the remiges of the tern (Sterna hirundo) especially 
favorable material for studying the formation of epidermal pigments. 
Their pigment cells attain a large size, are comparatively regular in 
contour, and very abundant. 
The first signs of pigment formation appear in certain of the “ inter- 
mediate cells ” of the fundament of the feather immediately before the 
differentiation of the ridges. The pigment arises in the form of grayish 
or light yellowish corpuscles, of exceedingly small size, arranged along 
delicate protoplasmic strands, which radiate from the nucleus and 
sometimes anastomose more or less with one another. These corpuscles 
increase rapidly in size and are soon large enough to be recognized with 
a 5 inch oil immersion lens as definite rod-shaped granules (Plate 6, 
Figs. 30, 31). At the same time they become deeper in color and 
more and more numerous until finally they form a complete ball, 
Plate 3, Fig. 16; Plate 6, Fig. 35, cl. pig.), which was often taken 
by the earlier writers to be a homogeneous mass. 
In the course of development these rods are easily seen to be radially 
distributed about the nucleus, an arrangement which has been described 
for the pigment cells and chromatophores of other animals. 
The nuclei of these pigment cells are entirely destitute of the pig- 
ment granules, a condition which Solger (89, ’90, ’91) also noted in 
the pigment cells of fishes and mammals. 
Kromayer (97), too, observed in the developing chromatophores of 
frog skin that the first appearance of pigment granules was along proto- 
plasmic strands; the granules were at first light in color, but gradually 
grew darker. 
Post (94, pp. 491, 492) found that melanin pigment granules have 
characteristic variations in shape and size for different animals. “ Die 
Pigmenttheilchen in den Oberhautgebilden verschiedener Thierarten 
sind ebenfalls sehr verschieden, z. B. bei der Katze lang und ziemlich 
dick, beim Hunde wetzsteinférming in der Mitte verdickt, beim Meer- 
schweinchen und Kaninchen kurz und dick, beim Rinde. ziemlich lang 
und schlank. Auch das Pigment der Taubenfedern besteht aus Staébchen 
von miissiger Grésse.” I have also found variations in size for the birds 
