FEATHERS AND PATTERNS
17
dominance). During the formation of the after-feather in the fowl, no
ventral mucopolysaccharide staining is shown in dermal papilla sections,
despite the existence of the ventral rachis. The dermal papilla of the emu
appears not to have been investigated in this regard. For information
about after-feather development, but not for argument, see Lillie and
Juhn (1938).
An explanation might be suggested with a somewhat different basis,
however. Cohen and 'Espinasse showed that after a pinfeather was
plucked the epidermal healing of the apex (to form the dome whose walls
are the collar) proceeds asymmetrically in the contour feather. The major
contribution is from the dorsal aspect, a tongue of epithelium reaching
over the top of the papilla and extending into ventral collar. This correlates well both with the staining reaction of the dorsal aspect of the
dermal papilla and with the effect of papillär extract on epidermal cells.
Figure 8 shows a healed profile with the normal directions of barb-ridge
orientation marked on the collar region. The correlation with the pattern
of healing in the papilla is quite suggestive. However, the same criticism
applies to this suggestion as to the theory of development suggested then.
The mechanism fits the regeneration after plucking perfectly; unfortunately, feathers are not usually plucked, but are lost after closure of the
inferior umbilicus, all of the collar having been "used up." In this case
there is no open top to the papilla which can heal asymmetrically
(compare Fig. 5), and any assumption that comparable asymmetry is
provided by "differential growth rates" or other embryological excuses
has not been proved, to say the least. One minor piece of evidence supports the view that barb-ridge obliquity is related to the asymmetry of
healing papillae in contour feathers. The down feather does not seem to
B. Part of the edge of a culture from Light Sussex pinfeather collar. Ridges
which probably started as a scalloped edge to the outgrowth are advancing into the
mass of the culture (upper, left) and are extending outward into the medium at
their free edges. Melanocytes are differentiating as the ridges become discrete.
C. Part of a section of a watchglass culture of pulp to which some collar was
adherent. At the lower edge fairly good barb ridges may be seen in section. At the
upper edge the overgrowing epithelium may be seen to be advancing as a series
of separate tongues, each of which is continuous with one of the ridges seen below.
This is reminiscent of the situation in A. (As is so often the case, all four pictures
in this figure derive from work in which the development of barb ridges was not
the primary objective, and each of these "accidental" cultures produced clearer and
more dramatic pictures than any of the carefully controlled series!)
D. Part of a live culture from Brown Leghorn breast feather collar which had
begun to make barb ridges at about 41 °C. The culture was then left on the bench
at room temperature for some hours and reexamined. Barb ridges are apparently in
chaos, neither their orientation nor their periodicity having "settled down."
17
dominance). During the formation of the after-feather in the fowl, no
ventral mucopolysaccharide staining is shown in dermal papilla sections,
despite the existence of the ventral rachis. The dermal papilla of the emu
appears not to have been investigated in this regard. For information
about after-feather development, but not for argument, see Lillie and
Juhn (1938).
An explanation might be suggested with a somewhat different basis,
however. Cohen and 'Espinasse showed that after a pinfeather was
plucked the epidermal healing of the apex (to form the dome whose walls
are the collar) proceeds asymmetrically in the contour feather. The major
contribution is from the dorsal aspect, a tongue of epithelium reaching
over the top of the papilla and extending into ventral collar. This correlates well both with the staining reaction of the dorsal aspect of the
dermal papilla and with the effect of papillär extract on epidermal cells.
Figure 8 shows a healed profile with the normal directions of barb-ridge
orientation marked on the collar region. The correlation with the pattern
of healing in the papilla is quite suggestive. However, the same criticism
applies to this suggestion as to the theory of development suggested then.
The mechanism fits the regeneration after plucking perfectly; unfortunately, feathers are not usually plucked, but are lost after closure of the
inferior umbilicus, all of the collar having been "used up." In this case
there is no open top to the papilla which can heal asymmetrically
(compare Fig. 5), and any assumption that comparable asymmetry is
provided by "differential growth rates" or other embryological excuses
has not been proved, to say the least. One minor piece of evidence supports the view that barb-ridge obliquity is related to the asymmetry of
healing papillae in contour feathers. The down feather does not seem to
B. Part of the edge of a culture from Light Sussex pinfeather collar. Ridges
which probably started as a scalloped edge to the outgrowth are advancing into the
mass of the culture (upper, left) and are extending outward into the medium at
their free edges. Melanocytes are differentiating as the ridges become discrete.
C. Part of a section of a watchglass culture of pulp to which some collar was
adherent. At the lower edge fairly good barb ridges may be seen in section. At the
upper edge the overgrowing epithelium may be seen to be advancing as a series
of separate tongues, each of which is continuous with one of the ridges seen below.
This is reminiscent of the situation in A. (As is so often the case, all four pictures
in this figure derive from work in which the development of barb ridges was not
the primary objective, and each of these "accidental" cultures produced clearer and
more dramatic pictures than any of the carefully controlled series!)
D. Part of a live culture from Brown Leghorn breast feather collar which had
begun to make barb ridges at about 41 °C. The culture was then left on the bench
at room temperature for some hours and reexamined. Barb ridges are apparently in
chaos, neither their orientation nor their periodicity having "settled down."