2
JACK COHEN
as well as structure; he even saw the pigment cells as a separate stock
from the other cells of the feather and debated their origin.
As experimental embryology developed, those interested in morphogenesis split into two major camps: (1) those concerned with the origins
of structures, and with early development until, say, the neurula of vertebrates, and (2) those concerned with the development, maintenance, and
coming to function of structures, their interest continuing into the adult
organism. Some of these latter were lost into endocrinology, just as some
of the former were lost via gametogenesis into genetics. However, the
schism has remained. For example, the transformation of the cleaving
egg into the organ-forming embryo has remained a no-man's-land for
the experimental biologist. There have been occasional heroic scouts and
advance parties, but no real encampments. Even the work on amphibians
of the last 20 years, associated with Moore (1960), with Briggs and
King (1959), and with Gurdon (1963), seems to have aroused controversy rather than to have provoked new work.
A very similar schism, too, is reflected in work on feather development.
One group of workers, led by Lillie and his school, followed the lead of
Davies and Strong, concentrating primarily on the feather in its follicle
(Lillie, of course, did describe the origin of feather germs in the skin,
but his main interest was surely in the definitive feather). Other workers,
perhaps notably Hardesty and Holmes, concentrated on the "real" embryology and concerned themselves primarily with origins of the follicles.
Much the same division is apparent throughout the work on hair. This
has led to a curious division in the literature. For example, in the early
1940's, Lillie and Wang were thought to have implicated the epidermis
as that tissue which controlled tract-specificity. Naturally, therefore, such
papers as those of Willier (1952) and Trinkaus (1953), concerned with
the feathers of birds out of the egg, assumed that everyone knew the
epidermis to be tract-specific. Cohen (1959) was also guilty. But for
many years embryologists had known of the influence of stroma on overlying epithelium. Even after SengePs elegant early work was published,
following the review by Cairns and Saunders (1954), there was still a
strong feeling that specificity in the adult resided in the epidermis, in the
embryo in the dermis. It was as if embryo and adult birds belonged to
different phyla. As an embryologist working primarily on interactions in
the adult, the author finds this schism particularly difficult to live with,
and has suggested (Cohen, 1965) a way out of this particular dilemma
which is now being checked in several laboratories.
Nevertheless, there are still too few who can tread the ground between
"How does it arise?" and "How is it maintained in a functional state?"
with any degree of confidence. The feather germ might well prove to be
JACK COHEN
as well as structure; he even saw the pigment cells as a separate stock
from the other cells of the feather and debated their origin.
As experimental embryology developed, those interested in morphogenesis split into two major camps: (1) those concerned with the origins
of structures, and with early development until, say, the neurula of vertebrates, and (2) those concerned with the development, maintenance, and
coming to function of structures, their interest continuing into the adult
organism. Some of these latter were lost into endocrinology, just as some
of the former were lost via gametogenesis into genetics. However, the
schism has remained. For example, the transformation of the cleaving
egg into the organ-forming embryo has remained a no-man's-land for
the experimental biologist. There have been occasional heroic scouts and
advance parties, but no real encampments. Even the work on amphibians
of the last 20 years, associated with Moore (1960), with Briggs and
King (1959), and with Gurdon (1963), seems to have aroused controversy rather than to have provoked new work.
A very similar schism, too, is reflected in work on feather development.
One group of workers, led by Lillie and his school, followed the lead of
Davies and Strong, concentrating primarily on the feather in its follicle
(Lillie, of course, did describe the origin of feather germs in the skin,
but his main interest was surely in the definitive feather). Other workers,
perhaps notably Hardesty and Holmes, concentrated on the "real" embryology and concerned themselves primarily with origins of the follicles.
Much the same division is apparent throughout the work on hair. This
has led to a curious division in the literature. For example, in the early
1940's, Lillie and Wang were thought to have implicated the epidermis
as that tissue which controlled tract-specificity. Naturally, therefore, such
papers as those of Willier (1952) and Trinkaus (1953), concerned with
the feathers of birds out of the egg, assumed that everyone knew the
epidermis to be tract-specific. Cohen (1959) was also guilty. But for
many years embryologists had known of the influence of stroma on overlying epithelium. Even after SengePs elegant early work was published,
following the review by Cairns and Saunders (1954), there was still a
strong feeling that specificity in the adult resided in the epidermis, in the
embryo in the dermis. It was as if embryo and adult birds belonged to
different phyla. As an embryologist working primarily on interactions in
the adult, the author finds this schism particularly difficult to live with,
and has suggested (Cohen, 1965) a way out of this particular dilemma
which is now being checked in several laboratories.
Nevertheless, there are still too few who can tread the ground between
"How does it arise?" and "How is it maintained in a functional state?"
with any degree of confidence. The feather germ might well prove to be