360 On the Pterylography of the Hoatzin. 



feathers '' neossoptiles/' In addition to this covering of neos- 

 soptiles, there is developed towards the end of the nestling- 

 period a second downy covering, which, for a time, bears a 

 considerable share — if not the greater part — in clothing the 

 bird. This second downy covering is composed of true down- 

 feathers or plumulse, and, so far as I am aware, such a covering 

 has never before been described in any nestling. 



In the wing of th6 nestling we have a revelation of pro- 

 found importance^ for, so it seems to me, through it we get 

 a glimpse into the phylogeny not only of its immediate allies, 

 the Gallinos, but possibly of the whole avian class. 



The first step in the direction of this discovery was made 

 by Mr. Quelch (12) when he found that the nestling of 

 Opisthocomus used its wings to assist it in climbing about 

 the trees in which its nest was placed. In a most valuable 

 and interesting paper he details with great clearness the 

 wonderful life-history of these birds. Suffice it here to say 

 that Opisthocomus is arboreal in the strictest sense of the 

 word, since it rarely, if ever, descends to the ground ; hence 

 the enormous feet and sternal callosity. Nidification is per- 

 formed in trees, apparently those overhanging the water for 

 preference. As I have already elsewhere written (11), 'Hhe 

 young .... instead of remaining in the nest until they are 

 able to fly, are in the habit, at a very early stage in their life, 

 of climbing out of the nest, it may be to gain a better coign of 

 vantage whence to meet the parents returning with food, or 

 to take refuge in more dense foliage to escape an enemy — 

 sometimes the one and sometimes the other cause impels 

 them to leave their home ; in either case it is obvious that 

 the chances of a fall are exceedingly probable. Now, as 

 might have been expected, these youngsters are particularly 

 capable of taking care of themselves, possessing not only 

 enormous feet fitted for grasj)ing — like the parents — but 

 they have powerful auxiliaries in the shape of the beak, 

 which is used much as is that of a Parrot in climbing, and 

 wings, which are armed with large claws on the first and 

 second digits. On turning to fig. 2, p. 361, it will be seen 

 that the general form of the wing renders such a mode of 



