312 The Development of Chromatophores in Necturus 
In sections of this stage one frequently finds conditions such as that 
represented in Fig. 3, in which the protoplasmic processes of the dermal 
chromatophores extend among the ceils of the epidermis. Other sections 
show widely branched chromatophores lying wholly within the epidermis, 
as shown in Fig. 4. From the study of sections alone, one would readily 
infer that these epidermal chromatophores are simply the dermal chromat- 
ophores which have wandered into the epidermis. I have ex- 
amined many sections with the hope of finding a chromatophore in which 
the cell body lay partly in the dermis and partly in the epidermis, but 
such a cell has not been found. All doubt, however, is dispelled by using 
the binocular microscope under which one can readily see the dermal 
chromatophores pass outward into the epidermis. 
In the epidermis one frequently observes the peculiar type of cells de- 
scribed under the preceding stage. These cells may be as yet unpig- 
mented or they may show varying degrees of pigmentation, often the 
pigment is confined to the region of the nucleus as shown in Fig. 5, d, 
again the pigment has extended to one or more of the cytoplasmic pro- 
cesses, as represented in Fig. 6, e. 
Larve 17-18 mm.—The chromatophores show a marked increase in 
number over the preceding stage. In a number of larve, they have ex- 
tended well down over the upper surface of the yolk. In the head re- 
gion there is a median dorsal line which is almost free from chromato- 
phores. On either side of this line chromatophores have extended down- 
ward to the upper margin of the nose and eye. The upper margin of the 
retina is now deeply pigmented,and not infrequently numbers of chromat- 
ophores are observed directly over the lens. They have extended to the 
base of the gills, although but few are seen in the gill bars. A few are 
present in the dorsal surfaces of both the anterior and posterior limbs. 
The dorso-lateral veins are present along the dorso-lateral surface of the 
yolk. Even at this early stage, the chromatophores are becoming more 
densely aggregated along the lines of these veins. Now as in the pre- 
ceding stages, one can see in the region sparsely pigmented a continual mi- 
gration of the dermal chromatophores from a deeper to a more superficial 
position. In those regions which are densely pigmented, one can readily 
see an increasing number of the dermal chromatophores passing into the 
epidermis. . 
Serial sections of this stage show a continued formation of the dermal 
chromatophores in the deep mesenchyme, and especially in the intermus- 
cular spaces. As they pass toward the surface the pigment extends into 
the cytoplasmic processes and they become more and more branched. 
The greater number of these chromatophores pass to the outer layer of 
