PASSERINE BIRDS OF NEW YORK 345 



Wray, R. S. 



'87 On the structure of the barbs, barbules and barbicels of a 

 typical pennaceous feather 

 Ibis, 5th ser., V. 1887. pp. 420-423, pi. XII 



Yarrell, W. 



'33 [Observations on the changes of plumage in birds.] 

 Proc. Zool. Soc. (London.) 1833. pp. 9, 10. 



Yarrell, W. 



'33 [On the laws that regulate the changes of plumage in birds.] 

 Proc. Zool. Soc. (London.) 1833. p. 56 



Yarrell, William 



'35 Observations on the laws which appear to influence the as- 

 sumption and changes of plumage in birds 

 Trans. Zool. Soc. (London.) I. 1835. pp. 13-19 

 [Preliminary mention in] Proc. Zool. Soc., I. 1833. 

 pp. 9, 10, 56. 



