1883.] 209 [Jeffries. 



out a most remarkable theory of growth for feathers ; the realiza- 

 tion of which it is difficult to find. He seems to think that the 

 various elements of the feather are formed by division from little 

 bulbs at the ends, each barb having its own bulb. 



Pernitza studied the development with considerable care, and 

 as far as he goes, my observations in the main agree with his. 

 The same may be said of the paper by Studer. Indeed, were it 

 not for the sake of uniformity and of new distinctions introduced 

 into the study of the epiderm the whole subject might be passed 

 over. 



Since feathers grow from the base many of the stages of devel- 

 opment can be found in any one of the larger papillae, but the 

 whole history of a feather cannot, as stated by some, be revealed 

 by any single papilla. There can be but one stage of each 

 part in any single papilla. But since all the papillae do not 

 develop at the same rate or even appear at the same time, nearly 

 all, if not all, the stages may be found on the body of any well- 

 advanced embryo. Accordingly I shall not trace the develop- 

 ment by age — but by stages. 



The first signs of the feathers appear about the sixth day of 

 incubation as small hemispherical papillae usually arranged in 

 quincunx order. They are composed of an inner core of meso- 

 dermal undifferentiated cells and the epiderm of only the two 

 primary coats. The papillae grow rapidly in length and at the 

 same time tend to sink below the surface, more especially at the 

 posterior side. By this means the papillae become inclined 

 toward the posterior end of the embryo. As each papilla slowly 

 elongates a capillary loop is formed in the mesodermal core and 

 the mucous cells produce a large number of transitional cells so 

 that the epiderm becomes quite thick. 



We now come to the first traces of the feather. Two thick- 

 enings of the epiderm (fig. 6 d) appear on the outer surface of 

 the papilla. These, starting from the top, slowly extend towards 

 the base of the papilla and encroach on the pulp. While these 

 thickenings, destined to form the first two barbs, are growing, 

 the epitrichial layer becomes more compact and the outer transi- 

 tional cells more or less fusiform and horny. By this change 

 they form a sort of sheath for the deeper parts of the epiderm. 



PROCEEDINGS B. S. N. H. VOL. XXII. 14 NOVEMBER, 1883 



