34
JACK COHEN
a period of 4 to 5 days. A similar simple theory of barring would be
much appreciated.
Unfortunately, no such explanation will serve for the production of
barb ridges. It seems at the moment that this is not a Turing situation,
but until the experiments are repeated under much more rigid conditions
no more should be said. Even if barb ridges are not produced in this
way, the concept of diffusing morphogens has been valuable in other
contexts and may well have validity in some real situations.
Patterns that register with one another are the most difficult of all to
theorize about. They obviously depend on all the other events in morphogenesis being absolutely predictable. Until we know a good deal more
of the factors controlling feather spacing, feather growth and replacement, and feather pigmentation, it would seem a little unwise to attempt
a theory of register.
Acknowledgment
I wish to thank Professor P. G. 'Espinasse for introducing me to the fascination
of feathers, and I wish to express my gratitude to the Royal Society for their
grant toward a major part of the expenses of the barb-ridge study. I also wish to
express my gratitude to Dr. G. Russell Coope for making the specimens in Figs.
2C and 13 available for photography; he informs me that they come from the
German variety of Accipiter
gentilis.
References
Allen, M. J. (1959). Embryological development of the Polychaetous Annelid,
Diopatra cuprea (Bosc). Biol. Bull. 116, 339-361.
Bell, E. (1965). Geometry of inactive and active polysomes of the developing down
feather. Submitted to Science.
Bell, E., Schuler, M., and Merrill, C. (1964). Feather formation and synthesis of
keratin by primary skin cells and by skin cells grown in vitro. In "The Epidermis" (W. Montagna and W. C. Lobitz, Jr., eds.), p. 35-56. Academic Press,
New York.
Ben-Or, S., and Bell, E. (1965). Skin antigens in the chick embryo in relation to
other developmental events. Develop. Biol, (in press).
Berrill, N. J. (1961). "Growth, Development and Pattern," especially pp. 310-352
and 403-411. Freeman, San Francisco, California.
Briggs, R. W., and King, T. J. (1959). Nucleocytoplasmic interaction in eggs and
embryos. In "The Cell" (J. Brächet and A. E. Mirsky, eds.), Vol. I, p. 537.
Academic Press, New York.
Bullough, W. S., and Laurence, Ε. B. (1964). The production of epidermal cells.
Symp. Zool. Soc. London 12, 1-23.
Cairns, J. M., and Saunders, J. W., Jr. (1954). The influence of embryonic mesoderm
on the regional specification of epidermal derivatives in the chick. J. Exptl.
Zool 127, 221-248.
Carter, H. B. (1965). Variation in the hair follicle population of the mammalian
skin. In "Symposium on the Biology of Skin and Hair Growth" (A. G. Lyne
and B. F. Short, eds.), p. 25-33. Angus and Robertson, Sydney.
JACK COHEN
a period of 4 to 5 days. A similar simple theory of barring would be
much appreciated.
Unfortunately, no such explanation will serve for the production of
barb ridges. It seems at the moment that this is not a Turing situation,
but until the experiments are repeated under much more rigid conditions
no more should be said. Even if barb ridges are not produced in this
way, the concept of diffusing morphogens has been valuable in other
contexts and may well have validity in some real situations.
Patterns that register with one another are the most difficult of all to
theorize about. They obviously depend on all the other events in morphogenesis being absolutely predictable. Until we know a good deal more
of the factors controlling feather spacing, feather growth and replacement, and feather pigmentation, it would seem a little unwise to attempt
a theory of register.
Acknowledgment
I wish to thank Professor P. G. 'Espinasse for introducing me to the fascination
of feathers, and I wish to express my gratitude to the Royal Society for their
grant toward a major part of the expenses of the barb-ridge study. I also wish to
express my gratitude to Dr. G. Russell Coope for making the specimens in Figs.
2C and 13 available for photography; he informs me that they come from the
German variety of Accipiter
gentilis.
References
Allen, M. J. (1959). Embryological development of the Polychaetous Annelid,
Diopatra cuprea (Bosc). Biol. Bull. 116, 339-361.
Bell, E. (1965). Geometry of inactive and active polysomes of the developing down
feather. Submitted to Science.
Bell, E., Schuler, M., and Merrill, C. (1964). Feather formation and synthesis of
keratin by primary skin cells and by skin cells grown in vitro. In "The Epidermis" (W. Montagna and W. C. Lobitz, Jr., eds.), p. 35-56. Academic Press,
New York.
Ben-Or, S., and Bell, E. (1965). Skin antigens in the chick embryo in relation to
other developmental events. Develop. Biol, (in press).
Berrill, N. J. (1961). "Growth, Development and Pattern," especially pp. 310-352
and 403-411. Freeman, San Francisco, California.
Briggs, R. W., and King, T. J. (1959). Nucleocytoplasmic interaction in eggs and
embryos. In "The Cell" (J. Brächet and A. E. Mirsky, eds.), Vol. I, p. 537.
Academic Press, New York.
Bullough, W. S., and Laurence, Ε. B. (1964). The production of epidermal cells.
Symp. Zool. Soc. London 12, 1-23.
Cairns, J. M., and Saunders, J. W., Jr. (1954). The influence of embryonic mesoderm
on the regional specification of epidermal derivatives in the chick. J. Exptl.
Zool 127, 221-248.
Carter, H. B. (1965). Variation in the hair follicle population of the mammalian
skin. In "Symposium on the Biology of Skin and Hair Growth" (A. G. Lyne
and B. F. Short, eds.), p. 25-33. Angus and Robertson, Sydney.