Pterylograpliy of the Hoatzm. 351 



Apt. al(B inferioris (PI. IX. fig. 3, Apt.a.inf.). — Embraces 

 the pre-axial border of the ventral surface of the arm and 

 patagium. 



Down-feathers : — 



These are distributed sparsely over the whole body ; but 

 on the head and upper part of the neck they are reduced 

 to the verge of extinction. On the trunk they are very 

 long, and more or less definitely arranged, so as to run in 

 double rows between two rows of contour-feathers (see 

 PI. X. figs. 2, 3, indicated by small dots). This rule, how- 

 ever, is by no means strictly adhered to, since it often happens 

 that down-feathers intrude themselves between contour- 

 feathers, i. e. run transversely to the general parallel lines. 



Pulvlplumes or Powder-down. — Absent. 



Filopluma. — One at the base, and to the outer side, of 

 every contour-feather. They are about half as long as their 

 respective contour-feathers, have a black shaft and light 

 yellow vexillum. Those accompanying the remiges are rather 

 larger and have a considerable vexillum. 



Structure of the Contour-feathers . — A noticeable feature 

 about the contour-feathers is their fewness and relatively 

 great length throughout the whole body. The individual 

 feathers preserve their pennaceous structure throughout to 

 a singular degree, inasmuch as the rami at the base of the 

 contour-feathers usually become more or less downy, whilst 

 here only the extreme edge of the vane or vexillum takes on 

 this downy structure. 



The aftershaft, though nearly half as long as the main 

 feather, has a short and very slender axis, bearing a few long 

 and delicate rami, the radii presenting the appearance of 

 minute setse along the shaft of the ramus. In the feathers 

 on the head the transition from contour-feathers to simple 

 bristles can be traced by a series of most perfect gradations. 



Structure of the Plumula. — The down-feathers form large 

 brush-like tufts, and possess both rhachis and aftershaft, 

 which is of considerable size. Microscopically the radii, 

 like the neossoptiles, have well-developed fila ; in this they 

 differ from the nestling plumulae, in which fila are rare. 



