INTEGUMENT OF NECTURUS MACULOSUS Fyitey 
e. Conclusion. According to Ehrmann (’92, ’96), all chromato- 
phores are differentiated from ordinary connective-tissue cells 
(melanoblasts), and some of them secondarily pass into the 
epidermis. The evidence furnished by these studies of Necturus 
gives no support to this hypothesis. In regenerating tissue the 
chromatophores are abundant in the epidermis before they 
develop in the dermis. Further, a study of the skin under normal 
conditions inclines one to favor Rabl’s theory of the leucocytic 
origin of the pigmented cells, while their behavior in regeneration 
and in transplantation experiments strongly suggests a relation 
to ordinary epithelial cells. 
At present, it is generally accepted that epidermal cells are 
capable of producing pigment. It is also known that in regener- 
ation they become amoeboid temporarily and migrate consider- 
able distances. In the formation of the large alveolar glands, 
epidermal cells may even move down into the dermis. More- 
over, it has been found by L. Loeb (’02) that epithelial cells in 
regenerating mammalian skin do actually take up blood cor- 
puscles and other solid particles. Hence, it would appear pos- 
sible that the specialized pigment cells found in the epidermis 
are not modified leucocytes, but deceptively similar epithelial 
cells which have become permanently amoeboid and often heavily 
pigmented, with the capacity of performing phagocytic duty. 
DERMIS 
A. Layers 
1. In other Amphibia. ‘The dermis exhibits in all Amphibia 
a division into several layers, due to the arrangement of the 
bundles of connective tissue. In most urodeles (Bugnion, ’73; 
Paulicki, ’85; Schuberg, ’03; Esterly, 04; Schuberg, ’07 c) it 
is divided into three layers—the outer compact, the intermediate 
spongy, and the inner compact. Also in the Anura three layers 
have been described, but the three regions designated do not 
always correspond with those of the Urodela. However, Stieda 
(65), P. Schultz (89), Weiss (99), Grénberg und Klinckowstrém 
(94), and Schuberg (07 a, b, ¢, ’08) have described three layers 
