Pterylography of the Hoatzin. 355 



Cubitals. — The proximal remiges still remain undeveloped, 

 being only represented by the neossoptiles. 



The contour of the wing has now changed, and the 

 post-axial margin has extended backwards towards the free 

 finger-tip ; this will be seen better in stage 5. 



Stage 5. The plumage is now made up partly of the pencil- 

 like tips of the definitive feathers^ and the neossoptiles, 

 attached to their tips, and partly of plumulae, which have 

 now attained considerable size. The neck, however, is still 

 but sparsely clothed. The down-feathers remain at about 

 the same grade of development as in stage 1. 



Pt. alaris (PI. XI. fig. 8) :— 



Primaries (P.). — As a reference to the figure will show, 

 these have now attained considerable dimensions, probably 

 sufficiently to serve on occasion the purposes of flight. 



Cubitals {C.r.). — The most proximal remiges have just 

 pushed beyond the post-axial margin of the wing, whilst, as 

 will be seen in tig. 3, the first remex of the series (the most 

 distal) is about equal in length to its major covert ; the rapid 

 decrease in length of these remiges from I backwards is well 

 seen in the figure, where only four remiges can be traced. 



Tectrices : — 



T. majores. — The dorsal row of these coverts (PI. XI. 

 fig. 3, C), like the remiges, is much further developed on the 

 manus than on the cubitus. 



T. media. — Just appearing on the hand and distal portion 

 of the forearm. The under surface of the wing is sparsely 

 clothed with long slender neossoptiles, but gives no further 

 evidence of the definitive feathers. 



III. Structure of the Neossoptiles and Plumulde. 



Neossoptiles (PI. XI. fig. 5, N,). — These are umbelliforra, 

 each consisting of some 15 rami, bound closely together at 

 their base and continuous below with the definitive feather 

 which it represents ; there is, as the term umbelliforra implies, 

 no rhachis, and not even, as is often the case, a calamus or 

 quill. These rami are produced into long filaments, which 



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