Fig. 2. 



Fig. 2. — The right wing of a nestling Opisthocomus ci'istatns, ventral 

 view, showing how that the 2ud digit (ii.) is produced heyond the 

 ala menibrana (P.m.), and that the development of remiges 8-10 

 has been arrested, so as not to interfere with the freedom of the long 

 finger when climbing. 



Fiff. 3. 



P.iri. 



Fig. 3. — The right wing of a nestling of a Common Fowl {Gallus hankiva), 

 an ally of Oj)istkocomi(s. Owing to the exchange of an arboreal for 

 a terrestrial habit, the niauus is gradually shortening. The pollex 

 only retains the claw. The 2nd digit projects but slightly beyond 

 the ala membrana ; but the development of the most distal remiges 

 is still arrested. 



Fiff. 4. 



P.m. 



Fig. 4. — The right wing of an adult Opisthocomus cristatus, ventral view. 

 Contrast with that of the young bird, and the manus will be found 

 to be shorter than the foreai'm ; the " pollex," or " thumb," is con- 

 siderably reduced, as is also digit ii. The claw may be seen on the 

 pollex as a slight wart (c). 1-10. Metacarpo-digital remiges, or 

 quill-feathers ; P.m. Ala membrana, or posterior wing-membrane ; 

 c. Claw. 



All the figui'es (2, 3, and 4) are original, and were drawn by the 

 writer from the actual specimens. They have been kindlv lent to 

 this Journal bv tlie Editor of ' Natural Science." 



