286 Mr. F. E. Beddard on the 



organ is the presence of a well-developed curved nail upon 

 both the pollex and the index. In the large number of spe- 

 cimens which I have examined the relative positions of these 

 two digits differ very considerably ; sometimes they are 

 parallel to each other, in other specimens opposed, and there 

 are various gradations between these two extremes. The 

 condition of the specimens quite bears out Dr. Young^s state- 

 ment that " both the thumb and [first] finger have the 

 power of ab- and ad-duction ; " and it is not surprising to 

 learn that the young birds make use of their wings in scram- 

 bling about, and dig their claws into the ground. 



It is highly interesting to find that the possession of these 

 claws on the thumb and first finger, which is an archaic cha- 

 racter found in but few birds ^, is oi functional importance in 

 the young Hoatzin. The claws in the adult are, as Dr. Young 

 correctly states, reduced to mere wart-like tubercles. 



The first reference to the external characters of the wing 

 in the young Opisthocomus is contained in a communication 

 addressed to the Chicago Academy of Sciences by Mr. Edward 

 M. Brigham, some selections from which have been printed 

 in this Journal f^ and I have been able, through the kindness 

 of Mr. Sclater, to read, an article upon the same subject pub- 

 lished in the ' Chicago Tribune ' of Oct. 1881. There is not, 

 however, any exact description of the wing, but the presence 

 of claws is noted. 



Pterylosis. 



After a careful study of the pterylosis of the adult bird, 

 as well as of the nestlings and unhatched young, I find 

 myself unable to agree with Nitzsch's description J and illus- 

 trations § of the pterylosis of Opisthocomus. 



* Tlie most recent paper on this subject is by Prof. Parker " On the 

 Development of the Wing in the Common Fowl," Phil. Trans. 188S. The 

 principal types are there mentiond in which there are one, two, or three 

 claws. 



t Ibis, 1885, p. 118. 



X ' Pterylography,' Engl, ed., by Sclater, p. 108. 



§ Ibid. pi. vii. figs. 12, 13. 



