Pterylography of the Hoatzin. 367 



sparsely feathered. The median apterion does not^ in fact, 

 commence until the carina sterni, and is here exceedingly 

 narrow, its width being precisely that of the carina; the 

 apterion is sharply marked here by a straight row of feathers 

 on each side; from this point the c/j/e/'iow is conspicuous 

 and of some breadth, and the two ventral tracts become 

 narrow, though connected by scattered feathering with the 

 femoral tracts. 



"The lateral ventral tracts unite with one another some 

 way in front of the cloacal aperture. 



'^ The spinal tracts do not show quite so regular an 

 apterion as in Nitzsch's figures ; indeed, the dorsal surface is 

 sparsely feathered all over, with stronger feathers here and 

 there, particularly anteriorly, where they form a strong 

 band, as figured by Nitzsch. 



" The humeral tracts are conspicuous, as figured by 

 Nitzsch. 



" In the nestling the condition is much the same, but the 

 down-feathers are more numerous." 



In the embryo " the ventral apterion is as conspicuously 



developed as in the adult bird On the dorsal surface the 



feathering appeared to be quite uniform, though sparse ; in 

 these young chicks the ventral feathering was much closer 

 than the dorsal." 



Dr. Gadow (3) briefly refers to the pterylosis of Opist/io- 

 comus as follows : — " Dunen auf den Rainen und zwisclien 

 den Conturfedern. Der ganze Hals ist befiedert, ohne Seiten- 

 rain. Unterflur von der Brust an getheilt, jederseits breit 

 beginnend, ohne Aussenast, allmahlich zum After zusaramen- 

 riickend und sicli verschmalernd. Dorsalflur zwischen den 

 Schultern aus jederseits zwei Reihen Federn bestehend, und 

 undeutlich gespalten, dann als schmaler, nur zwei Federn 

 breiter Streif, ohne Andeutung von Sattel bis zur Biirzel- 

 driise gehend." 



Later the same author writes (4), "Die Jungen .... sind 



mit einem sparlichen gebauten Erstlingsgefieder be- 



deckt," and again, " bei den ei'wachsenen Dunen sparlich 

 auf den Rainen und zwischen den Conturfedern stehen und 



