654 Mr. R. Slieltbrd on the Ptenjhsis of the 



XLI. — On the Pterylosis of the Embryos and Nestlings 

 of Centropus sinensis. By R. Shelfohd, B.A. (Curator 

 of the Sarawak Museum). 



(Plate XIII.) 



The most remarkable feature in the young of Centropus 

 sinensis is the clothing of long, white, thread-like structures, 

 most strongly developed and most densely disposed on the 

 dorsal surface of the head and body (Plate XIII.). Dissec- 

 tion and microscopical examination show these threads to 

 be enormous prolongations of the horny sheaths which 

 envelop the developing feathers, a narrow lumen extends 

 from the base to the tip of each, whilst the base of each 

 lumen, again, is occupied by a feather-papilla, situated below 

 the skin. In order to avoid unnecessary circumlocution 

 and repetition, I shall term these thread-like structures 

 trichoptiles. The skin in young nestlings and ripe embryos 

 is black, except between the rami of the mandibles and on 

 the belly ; the white trichoptiles stand out in striking con- 

 trast to this dark background, and give the young bird a 

 sufficiently remarkable appearance. 



The horny sheaths of a// the definitive feathers are not pro- 

 duced to form trichoptiles ; whilst, on the other hand, certain 

 areas occupied in the young nestling and embryo by tricho- 

 ptiles are in later stages devoid of feathers. To describe the 

 changes in shape and extent of the pterylai and apteria 

 during the passage from the trichoptile-clad embryo to the 

 adult is the purpose of the present paper. 



Thanks to the generosity of Mr. Charles Hose, who has 

 furnished me with several gradational examples^ the material 

 at my dispo&al can be divided, roughly speaking, into three 

 stages, though the divisions are not very well marked, 



A nearly ripe embryo with a total length of 92 mm. con- 

 stitutes Stage 1 (Plate XIII. A) ; a young nestling with a 

 total length of 112 mm, may be regarded as typical of 

 Stage 2 (Plate XIII. B, and figs. 1 & 2, p. 655) ; and nestlings 

 ranging from 125 mm. to 145 mm. fall into the third division,, 



