Pterylography of the Hoatzin. 857 



In stage 2 the region immediately in front of and sur- 

 rounding the sternal callosity, as also that portion of the 

 apt. raesogastrsei below this callosity to the umbilicus, bears 

 long filaments representing either down- or contour-feathers, 

 but these apparently disappear before hatching. The pt. spi- 

 nalis is continuous -with the pt. femoralis, the two fused 

 tracts extending backwards to the tail. The apterium be- 

 hind and below the external ear is relatively larger than in 

 the nestling or adult, since it seems to extend for a short 

 distance down the neck. 



The conditions obtaining in this second stage seem to 

 contradict what we find in the earlier embryo, nestling, and 

 adult, inasmuch as the apt. mesogastrcEi is very narrow and 

 gives promise of being clothed with either definitive or down- 

 feathers ; the sj)inal and femoral tracts occupy a larger area 

 and are confluent, and the space below the external ear 

 extends down to the neck. I am inclined to consider that 

 the embryo feathers on the apt. mesogastrcei should be re- 

 garded as representing definitive rather than down-feathers, 

 in that, these excepted, there are no traces of down-feathers 

 visible on the body ; the down-papillae having now sunk below 

 the surface, the feather itself will not make its appearance 

 till after incubation. 



Rhamphotheca. — In some of the older embryos the conical 

 elevations on the inner side of the rhamphotheca (p. 356) 

 can be plainly discerned ; in addition, I find on the tip of 

 both upper and lower jaws a remarkable papillated pad, 

 which I propose to submit to a careful microscopic examin- 

 ation, the results of which I shall submit to the readei's of 

 ' The Ibis,' together with some other observations on the 

 tooth-like structures on the rhamphotheca of the nestling 

 Tinamou described in my last paper ('Ibis,' 1895, p. 1). 



Let us now collect and analyze such of the foregoing state- 

 ments as will enable us to express briefly the chief charac- 

 teristics of the pterylosis of Ojnsthocomus, as well as those 

 which appear to be new in connection with the present paper. 



The main features about the pterylosis of Opisthocomus 



