INTEGUMENT OF NECTURUS MACULOSUS 509 
leave no doubt as to their amoeboid character. However, they 
do not always occupy vacuoles, but are often found migrating 
through the tissue. Preparations made from regions which had 
previously been injured show them, along with polymorphonu- 
clear leucocytes, in the immediate vicinity of the blood clot, 
ingesting red corpuscles. Pigmented cells are also found among 
the epithelial cells of developing glands (fig. 19) and in the lumen 
of large granular glands (fig. 22) after these discharge (Nirenstein, 
708). In the last position they, in company with many leuco- 
cytes, are engaged in phagocytosis. At other times they are seen 
in the loosely woven tissue of the dermis, and in a very few cases 
have been found partly in the outer compact layer and partly 
within the epidermis (Rabl, 94; Prowazek, ’01). Only one case 
of mitosis was observed in these cells, the dividing cell containing 
considerable pigment as well as several nuclear fragments. 
The foregoing observations on the pigmented cells appear to 
support Rabl’s belief that the epidermal chromatophores have 
a leucocytic origin. They at least exhibit many of the char- 
acteristics of leucocytes and contain pigment only when they 
are in a pigmented region. In the white ventral tissue they 
never contain melanin, but bear a close resemblance to the large 
phagocytic cells described in the digestive epithelium. Still, the 
evidence is not conclusive. 
Winkler (10a; Triton and Salamandra) believes that the 
epidermal chromatophores arise by a differentiation in situ of 
ordinary epithelial cells, which elaborate pigment, become 
amoeboid, and send out long branching processes. He regards 
all of the pigmented cells of the epidermis as belonging to one 
class and does not recognize two types such as Eycleshymer 
(06 a) has described in Necturus. Furthermore, according to 
Winkler, these metamorphosed epidermal cells may migrate 
downward and enter the dermis. Thus we have two diamet: ically 
opposed views (Rabl, ’94; Winkler, 710 a) regarding the origin of 
chromatophores, and it does not seem possible to end the con- 
troversy by a study of fixed material alone, since the conditions 
found can be interpreted in either way. We must therefore 
rely on experimental evidence and direct observation of living 
material for a final settlement of the question. 
