F E A T H E R S A N D P A T T E R N S
13
The origins of the down feather in the skin of the chick embryo and
the differentiation of follicles have served as basic experimental material
for a number of workers. Hamilton (see review, 1965) has investigated a
variety of chemical and enzymatic conditions in vitro and has given
us some understanding of the histochemistry of the differentiation of
the feather germ. An approach more in line with modern embryological
techniques is t h a t of Moscona and his school (e.g., Garber and Moscona,
1963), who have investigated the reconstitution of embryonic skin from
cell suspensions in culture and on the chorioallantoic membrane. They
have found t h a t feather germs m a y be perfectly reconstituted in suspensions of pure chick cells, but t h a t the addition of more than a very
small proportion of mouse cells to the suspension prevents reconstitution
(Moscona and Moscona, 1965).
FIG. 5. Section of the skin of a 12-day Brown Leghorn chick neck. The cylinder
of the first juvenile feather generation is bearing the down feather on its tip. The
barbs of the down feather are sectioned along their length, but the barb ridges
of the juvenile feather are at a slight angle to the generators and show as bulges
in the cylinder wall.
The development of the feather is probably best considered as a twostage process: the papilla produces a collar, and the collar then elongates into a feather. The down feather of the embryo and young chick in
time is replaced by the contour feather. [Other t h a n purely descriptive
accounts of this transformation, such as, for example, Davies (1889),
Strong (1902), 'Espinasse (1939), and Lillie (1942), are not to be found
in the literature. However, it m a y be t h a t Trinkaus' " i m m a t u r i t y " view
is relevant also to this problem. This is discussed further in Section IV.]
The barbs of the down feather lie along generators of the feather cylinder (Fig. 5 ) . Those of the contour feather lie at a slight angle to these,
with their proximal ends nearer the dorsal (rachis) side of the cylinder
13
The origins of the down feather in the skin of the chick embryo and
the differentiation of follicles have served as basic experimental material
for a number of workers. Hamilton (see review, 1965) has investigated a
variety of chemical and enzymatic conditions in vitro and has given
us some understanding of the histochemistry of the differentiation of
the feather germ. An approach more in line with modern embryological
techniques is t h a t of Moscona and his school (e.g., Garber and Moscona,
1963), who have investigated the reconstitution of embryonic skin from
cell suspensions in culture and on the chorioallantoic membrane. They
have found t h a t feather germs m a y be perfectly reconstituted in suspensions of pure chick cells, but t h a t the addition of more than a very
small proportion of mouse cells to the suspension prevents reconstitution
(Moscona and Moscona, 1965).
FIG. 5. Section of the skin of a 12-day Brown Leghorn chick neck. The cylinder
of the first juvenile feather generation is bearing the down feather on its tip. The
barbs of the down feather are sectioned along their length, but the barb ridges
of the juvenile feather are at a slight angle to the generators and show as bulges
in the cylinder wall.
The development of the feather is probably best considered as a twostage process: the papilla produces a collar, and the collar then elongates into a feather. The down feather of the embryo and young chick in
time is replaced by the contour feather. [Other t h a n purely descriptive
accounts of this transformation, such as, for example, Davies (1889),
Strong (1902), 'Espinasse (1939), and Lillie (1942), are not to be found
in the literature. However, it m a y be t h a t Trinkaus' " i m m a t u r i t y " view
is relevant also to this problem. This is discussed further in Section IV.]
The barbs of the down feather lie along generators of the feather cylinder (Fig. 5 ) . Those of the contour feather lie at a slight angle to these,
with their proximal ends nearer the dorsal (rachis) side of the cylinder