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CHARLES
Ε.
WILDE
and a general attraction. Since these are derived from a variety of
experiments and have been developed by several different investigators,
they are probably not mutually distinct or exclusive agencies. However,
a heptafactorial system is indicative of the fact that the underlying
mechanisms of pro-pigment cell migration have yet to be made clear.
The problem of reserve melanoblasts remains to be discussed. There is
at present no evidence whether this group of cells migrates with the
initial neural crest dispersal in early embryogenesis or whether a more
prolonged migratory period occurs. Furthermore, the locus of reserve
cells is poorly established in lower vertebrates and with the exception
of hair follicles, feather germs and perhaps nevi, is not well established
for higher vertebrates. There is at present no fully accepted means for
the identification of unpigmented reserve cells, nor is their rate of cell
division or differentiation understood. This fact complicates the interpretation of pigment patterns particularly in later stages of development.
Pigmentary changes in adulthood are well known to be influenced by
hormonal effects, by specific disease states, trauma, inflammation and
subsequent repair, as well as other more poorly documented factors.
There exists in this field the nucleus for much more fruitful analysis.
V. The Causal Analysis of Pigment Cell Differentiation
The protoplasmic unit which differentiates both in vivo and in vitro is
the cell. Regardless of impedances and inhibitions referable in part to the
genetic endowment of the cell and to the micro-environment, differentiation is expressed in the cell itself or in its products. Differentiated
tissues are made up of cells in varying types and degrees of differentiation.
The analysis of pigment cell differentiation must ultimately be concerned with the dynamics of the protoplasmic units involved. The
nucleus of the cell is today considered to be the seat whence initiatory
influences order the biochemical syntheses of the cell. Metabolic
variants have been studied extensively on an organismal basis but only
rarely with regard to a specific differentiating cell type. The student of
differentiation must, however, concern himself with the specific metabolism of specific cell types.
An immediate problem which obtrudes is found in the relative roles
played within the cell by its genetic continuum (the nucleus) and its
cytoplasmic constituents. What is the role of the nucleus in differentiation? What is the role of the cytoplasm, so obviously the final seat of
differentiative processes?
With regard to the differentiation of pigment cells in urodeles, the
author has recently obtained data which indicates that the contemporary
presence of the nucleus is unnecessary for certain differentiative pro-
CHARLES
Ε.
WILDE
and a general attraction. Since these are derived from a variety of
experiments and have been developed by several different investigators,
they are probably not mutually distinct or exclusive agencies. However,
a heptafactorial system is indicative of the fact that the underlying
mechanisms of pro-pigment cell migration have yet to be made clear.
The problem of reserve melanoblasts remains to be discussed. There is
at present no evidence whether this group of cells migrates with the
initial neural crest dispersal in early embryogenesis or whether a more
prolonged migratory period occurs. Furthermore, the locus of reserve
cells is poorly established in lower vertebrates and with the exception
of hair follicles, feather germs and perhaps nevi, is not well established
for higher vertebrates. There is at present no fully accepted means for
the identification of unpigmented reserve cells, nor is their rate of cell
division or differentiation understood. This fact complicates the interpretation of pigment patterns particularly in later stages of development.
Pigmentary changes in adulthood are well known to be influenced by
hormonal effects, by specific disease states, trauma, inflammation and
subsequent repair, as well as other more poorly documented factors.
There exists in this field the nucleus for much more fruitful analysis.
V. The Causal Analysis of Pigment Cell Differentiation
The protoplasmic unit which differentiates both in vivo and in vitro is
the cell. Regardless of impedances and inhibitions referable in part to the
genetic endowment of the cell and to the micro-environment, differentiation is expressed in the cell itself or in its products. Differentiated
tissues are made up of cells in varying types and degrees of differentiation.
The analysis of pigment cell differentiation must ultimately be concerned with the dynamics of the protoplasmic units involved. The
nucleus of the cell is today considered to be the seat whence initiatory
influences order the biochemical syntheses of the cell. Metabolic
variants have been studied extensively on an organismal basis but only
rarely with regard to a specific differentiating cell type. The student of
differentiation must, however, concern himself with the specific metabolism of specific cell types.
An immediate problem which obtrudes is found in the relative roles
played within the cell by its genetic continuum (the nucleus) and its
cytoplasmic constituents. What is the role of the nucleus in differentiation? What is the role of the cytoplasm, so obviously the final seat of
differentiative processes?
With regard to the differentiation of pigment cells in urodeles, the
author has recently obtained data which indicates that the contemporary
presence of the nucleus is unnecessary for certain differentiative pro-