On the Normal and Abnormal Development of the Feather

Abstract

ABSTRACT A brief résumé is given of previous views of feather development. It is here emphasized that the collar is not to be regarded as producing a feather, but that it is in its entirety transformed into a feather and so is lost each time a feather is plucked. The culture of collar fragments is described. Many cultures produced apparently normal barbs and barbules without any process resembling concrescence. It is concluded that the only movement of tissue which occurs during the transformation of a collar into a feather is along the generators of the feather cylinder. The growth process concerned in the transformation of collar into feather is thus an essentially simple one of elongation such that distal collar becomes distal feather and proximal collar becomes proximal feather. It is the original length from distal collar to proximal collar that increases to become the whole length of the feather. Thus the structure of a particular feather may be projected back in a simple manner and the structure of the collar which it once was can be deduced. The collar, however, is indeed produced from the papillar ectoderm and the manner of its production is considered as a topological problem. A feather with a distal abnormality but which is normal proximally, resulting from a collar that is abnormal distally but normal proximally, may be repeated. The papilla in this case must return to a condition of abnormality after producing the normal proximal part of each such collar in order subsequently to produce another collar with a similar abnormality distally. From the results of papilla transplant experiments described here and from those reported from other workers, it is deduced that the manner of the production of a collar from a papilla involves a preferential growth of dorsal ectodermal tissue : tissue which was dorsal on the papilla grows over the top and down the ventral side of the dome produced at the top of the healing papilla. Some evidence is presented that this occurs both when a pin-feather is plucked and when a feather matures normally by closure of its inferior umbilicus. ‘Longitudinal’ and ‘transverse’ chimaerae, double feathers and feathers with defective apices, and their repetition, are considered and explained in terms of our views.