FEA THERS 245 



is beset with two series of numerous radii, forming a fluffy plumage 

 which is still more characteristic of the young in AccijLntres, Fasseres, 

 I'sittaci, and Striges. 



(3) In Gallinai there are from 10 to 12 somewhat stiff radius- 

 bearing rami, springing from a slender rhachis. 



(4) In Anseres a feeble rhachis bears all the biserially radiated 

 rami, forming feathers which closely resemble the Downs of mature 

 birds, and are devoid of an Aftershaft. 



The Neossoptiles differ much in the various groups of 

 liatitx. In Struthio they attain a length of 10 cm., and consist of 

 a calamus 1 cm. long, which may carry as many as 30 rami, each 

 biserially beset Avith radii, and these again are furnished with cilia. 

 The distal part of some of the rami is flattened and bears no radii. 

 In the absence of any trace of rhachis these feathers agree with 

 our second type. In lihea the Neossoptiles measure 6 cm. in 

 length and are composed of a feeble shaft carrying numerous rami 

 with their radii — the tips of the former being split into two or 

 three thickened ends. In Casuarius each primitive feather consists 

 of a long and slender rhachis bearing two series of rami, and con- 

 sequently resembling exactly one-half of the double Final feather. 

 In Dromaius each Neossoptile, which may be 4 cm. long, has a 

 short calamus carrying a long dorsal rhachis and a much shorter 

 ventral Aftershaft — each of them furnished Avith from 5 to 9 rami 

 measuring from 1 to 2 cm. in length, and these again beset Avith 

 numerous radii Avithout cilia. This is the only known instance of 

 a Neossoptile with an appendage, and it is significant that the 

 latter is smaller than the principal shaft, and only in its final stage 

 equals the rhachis in size. 



If Ave consider the condition of the various types of Neosso- 

 ptiles, above described, Avith reference to the presence or absence 

 of an Aftershaft in the Teleoptiles, Ave are led to conclude that 

 this appendage, and consequently ,.,-t3=lfF^ 



also the double feathers of certain .y^^^^^^^y 



Ratitx, are secondarily acquired ^.^^^^^'-^'-^f^^cM^^'^ 



and not primitive features. ^2^5^^$^^;^' .j'V^ 



The first indications of _f eathers '^^^i^^^^^::^ ^ 

 appear about the fifth or sixth day 'T ^J^-^^i^x^s^ '-j^ ' 



of incubation as slight pimples on P -^ 



the still semi-transparent skin of longitudinal Section of an early 



,1 T TT" 1 • 1 • Feather-papilla. Magnified. 



the embryo. ii,ach pmiple is pro- „„.,.,. ,,,,,. i. 



"' ri 111 ^1 Bpitncnium ; iV, Malpighian cells; 



duced by a cluster of dermal cells, p_ puip . sx. stratum comeum ; *, Place 

 covered by a feAV layers of epi- wliere the Malpigluan cells grow downward 



dermal cells, the outermost of *« form the foiiicie. 

 which forms a single layer of flattened cells, the epitrichium, AA^hile 

 the rest, the stratum Malpighii projjer, are cylindrical and soon 

 increase to form several layers. All the cells of the whole 



