INTEGUMENT OF NECTURUS MACULOSUS 507 
blood corpuscles from whose haemoglobin the pigment is derived. 
The pigmentation may occur early, before the cells have reached 
the epidermis, or later, after they have come to lie within it. 
Hooker (14) cultured in plasma epidermal cells from frog 
embryos 3 to 4 mm. long. Pigment appeared in many cells 
which then migrated down into the culture and assumed a 
stellate form by sending out pseudopodia. He states: ‘“‘Whether 
these cells remain as permanent pigment cells of the adult frog 
epidermis is uncertain and even questionable.”’ Later (15) he 
concludes that this pigment, elaborated by the embryonic epi- 
dermal cells, may exist for a time, but gradually disappears and 
the melanophoric cells found in the epidermis of older frog 
larvae are certainly mesodermic in origin. 
Eycleshymer (’06b) studied the differentiation of the epi- 
dermal chromatophores in the living larvae of Necturus. He 
observed them under the higher powers of a binocular micro- 
scope and was able to follow their movements accurately. He 
finds two kinds of chromatophores. “One is but slightly 
branched, taking on in general a pyramidal form. The other 
is highly branched, taking on a mossy appearance. The former 
becomes pigmented in situ within the epidermis. They may be 
mesenchymal cells which have wandered into the epidermis 
before becoming pigmented or they may be modified epithelial 
cells. The second type is derived from the mesenchymal cells 
which wander into the epidermis after becoming pigmented.”’ 
b. Conditions in normal tissue. In the adult animals I found 
no difficulty in recognizing the two types of pigmented cells 
described by Eycleshymer, but frequently intermediate con- 
ditions occur which make it appear probable that these cells 
have an identical origin. The pyramidal cells, or wandering 
cells of other writers, often contain little pigment and they may 
be completely rounded or possess distinct processes. But the 
most striking feature of many is the presence of large clumps of 
extraneous protoplasmic or nuclear material within their cell 
bodies, indicating phagocytosis (figs. 3, 4). This, coupled with 
the entire absence of pigment in the pyramidal cells of the white 
ventral region of the body, suggests some relationship between 
