THE WING OF ARCH^OPTERYX. 357 



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fact that no trace of the base of the quills can be seen, as well as explain 

 the facts noticed by Dr. Hurst when examining the fossil. Thenoles 

 which he has kindly sent me contain the following passage : 

 " Feathers along outer side of ulna not cut away but apparently 

 shifted (through decay of muscles, etc.) so as to lie in same horizon 

 as axis of ulna in greater part, but distally, somewhat lower and 

 distinctly beneath the three visible digits." 



Supposing, however, that we are looking at the dorsal surface ; 

 then it is not quite easy to see how it is that no trace has been left of 

 the base of the quills resting on the skeleton, for I am told these have 

 not been cleared away to expose the bones. By way of complicating 

 matters, we have to explain the semiplumous feathers before referred 

 to. I think it is evident that these cannot be the homologues of the 

 major coverts previously mentioned. In the first place, chiefly 

 because they not only cross the quills at a considerable angle, 

 but extend beyond them to the tip of the II. digit. They must, 

 then, represent some one or other of the series above the major 

 coverts. Unlike the quills, which would scarcely seem to differ from 

 those of modern birds, these coverts, in their length and texture, 

 depart from the normal habit of dorsal coverts, and resemble rather 

 the ornamental plumes such as decorate the wings of Cotinga pompadova. 



The crucial test, to my mind, to decide which of the two surfaces 

 we are deaUng with, is that of the overlap of the feathers; thus, if we 

 are looking at the dorsal surface of the wing, then the feathers 

 should have a distal overlap, i.e., the free edges of all the feathers will 

 be outwards; if at the ventral, then we ought only to see one broad 

 vane, not two as in the upper surface, and that vane the inner, so that 

 its free edge will be proximal or inwards. Whether or not I have a 

 defective vision remains to be proved, but I feel persuaded that we 

 have the dorsal surface presented to us, and not the ventral. If the 

 reader will note the direction of the light from which the photograph 

 was taken he will find that the distal vane of every feather is lit up, 

 while the proximal vane is in shadow ; further, it will be seen that 

 mud has drifted in between some of the feathers, e.g., 5 ; which, 

 reflecting the light, sharply defines the outer vane of one feather from 

 the proximal immediately under it. 



In order, however, to prove this point if possible, I have taken a 

 cast of a sparrow hawk's wing. This I propose to have photo- 

 graphed, illuminating it from the same direction as that of the Berlin 

 photograph, when we shall, I imagine, gain precisely the same effects 

 of light and shade. 



Now let us consider the probable function of the claws and 

 power of flight in Archaeopteryx. 



In fairness to myself, I must beg the reader to follow me a short 

 space off the beaten track, in order that we may discuss what seems a 

 rather important piece of evidence in support of the theory I wish to 

 propound. 



