INTEGUMENT OF NECTURUS MACULOSUS 493 
The ventral surface of the body exhibits considerable variation 
in pigmentation. Often it is completely pigmented, but not so 
densely as the dorsal surface. Sometimes there is a distinctly 
lighter median area; at other times, a sharply defined narrow 
white line is present. In a few animals the entire venter, from 
the cloaca to the gular fold, is white, lightly flecked by a few 
scattered melanophores, which are usually distributed along the 
lateral margins. The color pattern of the larvae is strikingly 
different from that of the adults. The most conspicuous feature 
in larval pigmentation is the two broad dorsolateral bands of 
pure yellow which run the entire length of the body and extend 
even to the tip of the tail. The contrast of yellow and black, 
which is vivid in the young animals, becomes subdued in the 
adults, and in some cases disappears almost completely. 
EPIDERMIS 
A. General description 
The epidermis is a stratified epithelium having from two to 
eight layers of living cells (figs. 1, 6, 12). The cells of the lower 
layer, in contact with the dermis, are tall columnar and constitute 
the germinative layer. The several layers above this are com- 
posed of the ordinary polygonal cells, showing no differentiation 
in size or form. Resting upon these transitional layers is a 
specialized stratum of cells known as the cuticular layer, the 
cells of which have on their outer surfaces a peculiarly differ- 
entiated zone generally referred to as the cuticular margin: 
(figs). 
The thickness of the epidermis, except in the gular fold region 
(fig. 16), varies but slightly throughout the entire body. The 
greatest thickness is found on the hands and feet, where there 
is developed a distinct stratum corneum (fig. 11) not found 
elsewhere. On the head and body practically no differences in 
thickness appear. On the dorsal and ventral edges of the tail 
there is a small reduction in number of the cell layers, but the 
maximum reduction occurs in the gular fold region, where the 
epidermis is only two or three cells thick. Concentric with the 
