372 On the Pterylography of the Hoatzin. 



Fig. 2. — Ventral aspect of same, showing the arrangement of the pterylae. 

 The shaded parts represent apteria. 



Additional Letters. 

 Apt.t.lat. Apterium trunci laterale. 

 Aiit.m. „ mesogastraei. 



Pt.a. Pteryla ani. 



Pt.v. „ ventralis. 



St.cal. Sternal callosity. 



Fig. 3. — Right-side view of same. The shaded parts as before. 



Additional Letters. 

 Apt.a.inf. Apterium alse inferioris. 

 H. Hypopteron. ' 



Plate X. 

 Fig. 1. — Dorsal aspect of a nestling Opistlwcomtis crtstatus, showing the 

 arrangement of the pterylae. The shaded parts represent the apteria. 



Letters as in Plate IX. 



Fig. 2. — Ventral aspect of the same. The very small dots are intended 

 to indicate approximately the distribution of the plumulae or down- 

 feathers. 



Um. Umbilicus. Other letters as in Plate IX. 



Fig. 3. — Right side of the same. The small dots, as in fig. 2, indicate the 

 distribution of the plumulse. 



Letters as before. 



Plate XI. 



Fig. 1. — Left wing of a nestling of the Common Fowl, dorsal view, 

 showing how, whilst the development of the proximal metacarpo- 



