INTEGUMENT OF NECTURUS MACULOSUS 505 
the epidermis on the ventral surface, and in most cases none at 
all is present, although there may be considerable pigment in 
the dermis. Pigment occurs in the ordinary epithelial cells (fig. 
1), but it is also contained in specialized cells (figs. 1, 2, 3, 4). 
The cylindrical cells of the germinative layer never contain 
pigment granules, but in all the cell layers above, collections of 
black or brown granules are commonly seen and they are nearly 
always found round the pole of the nucleus which is directed 
toward the outer surface (fig. 1). In the cells of the cuticular 
layer the pigment lies between the nucleus and the cuticular 
margin, and is often present in this position when pigment is 
lacking in the deeper epithelial cells of the same region. There 
can be no relation between the granules of pigment and the 
cuticular granules already described as staining readily in resor- 
cin-fuchsin, for the cuticular granules are found in the outer 
layer in all regions of the body, while pigment is often lacking 
in this layer, especially on the venter. 
Meirowsky (’06), in his experimental studies on the formation 
of epidermal pigment under artificial light, found that the 
granules first appeared uniformly around the nucleus, but later, 
under the influence of continued illumination, they moved and 
assembled themselves around the pole of the nucleus nearest the 
source of light. These results indicate that the distal distri- 
bution of pigment about the nucleus in normal tissue is probably 
determined by light. 
Lying in the intercellular spaces of the transitional layers 
are numerous highly branched chromatophores (figs. 1, 2, 12). 
They have small oval bodies consisting of the nucleus. and a 
small zone of cytoplasm, which is usually obscured by the pig- 
ment. Cells of this type are seldom found in the germinative 
layer, but their processes often extend far down between the 
cylindrical cells. 
Besides the highly branched forms, other cells, more rounded 
in appearance and resembling contracted chromatophores, occur. 
They lie in spherical spaces in the epidermis, and, since they 
seldom fill these spaces, they give a pitted appearance to the 
tissue as seen in perpendicular section. ‘Their nuclei are often 
