506 A. B. DAWSON 
slightly indented and usually eccentric. The abundant proto- 
plasm stains but lightly and is strewn with pigment granules. 
In many places short processes, sometimes with, sometimes 
without pigment, extend from the cell body to the surface of the 
space, and frequently they can be traced for some distance into 
the intercellular spaces. In these cells occur all variations from 
a densely pigmented condition to one in which only a few scat- 
tered granules are found. 
2. Origin of pigment cells. a. Literature. The question re- 
garding the origin of pigment in the epidermis of vertebrates 
is one of deep interest, and many investigations of the subject 
have been carried out on Amphibia both by students of histology 
and of pathology. The problem resolves itself into one primarily 
of relationships. What relation exists between ordinary epithelial 
cells, epidermal chromatophores, wandering pigmented cells, 
true leucocytes, and dermal melanophores? 
Some writers hold that the epidermis is of itself unable to 
elaborate any melanin and that the pigment present is of mesen- 
chymal origin (K6lliker, ’87; Ehrmann, ’92, ’96). Reinke (’06) 
suggests the possibility of pigment being deposited within the 
epidermal cells by other wandering cells. Negre (06) and Borrel 
(13) also report an invasion of the epidermis by pigment from 
the dermal melanophores. 
Many others, however, regard the epidermis as capable of 
forming pigment (Jarisch, 92; Rabl, 94; Rosenstadt, ’97; Pro- 
wazek, ’01; Loeb and Strong, ’04; Grund, ’05; Winkler, ’10 a; 
L. Loeb, ’11; Hooker, ’14 ¢, 715), but they are not in agreement 
as to the extent to which this activity may be carried on by the 
epithelial cells. Some regard only the pigment in the ordinary 
cells as of epidermal origin, believing the specialized cells to have 
migrated into the epidermis (Rabl, 94; Eycleshymer, ’06; Hooker 
15). A few consider the epidermal chromatophores to be meta- 
morphosed epithelial cells which have differentiated in situ 
(Jarisch, 92; Grund, ’05; Winkler, *10 a). 
According to Rabl (’94), all of the special pigmented cells in 
the epidermis are modified leucocytes. ‘The nuclear and cyto- 
plasmic fragments in their bodies are fragments of ingested red 
