566 A. B. DAWSON 
Epidermal pigmentation 
1. Pigment may be present in ordinary epidermal cells. Col- 
lections of black granules are often found around that pole of 
the nucleus which is directed toward the outer surface. 
2. The special pigment-bearing cells of the epidermis are of 
two apparently distinct types, 1) pyramidal and, 2) highly 
branched. ‘There is some evidence that the two types may be 
but contraction and expansion phases of one kind of cell. 
3. The epidermal chromatophores are not derived from those 
of the dermis. 
4, Pyramidal cells often contain fragments of extraneous chro- 
matin and cytoplasm, suggesting that they are of leucocytic origin. 
5. In regeneration and transplantation experiments the epi- 
dermal chromatophores behave like epidermal cells. Specialized 
pigment cells may perhaps be produced by a metamorphosis of 
ordinary epidermal cells. 
Dermis 
1. The dermis is arranged in three layers, an outer compact 
layer, an intermediate spongy layer, and an inner compact layer. 
2. Elastic fibers, both parallel and perpendicular to the sur- 
face, occur in the inner compact layer of the dermis. In the 
intermediate spongy region the elastic fibers are irregularly 
arranged, following in general the course of the connective-tissue 
bundles. None are found within the thin outer layer. 
3. Melanophores and xanthophores are present in the dermis. 
The melanophores are usually arranged in two layers, one layer 
being immediately beneath the outer compact stratum, the 
other beneath the inner compact stratum. The xanthophores 
are commonly found with the melanophores of the outer layer. 
Changes in coloration | 
1. Changes in the coloration of Necturus are produced by the 
contraction and expansion of the dermal melanophores. 
2. In bright light the melanophores are always completely 
expanded. 
