1894- THE BIRD'S FOOT. 211 



wing feathers. -^ And this average wing is particularly characteristic 

 of the Passerines and of most of their allies, which, as has long been 

 known, present a general structure most marked by the absence of 

 special peculiarities. In certain respects, indeed, their specialisation 

 fairly entitles them to their usually conceded place at the head of the 

 avian tree ; but their broad outlines are those of a simple and 

 primitive form. In this respect, as I pointed out in my previous 

 paper, they show some analogy to the Primates among Mammals. 



This brings me to my second point. Mr. Lucas suggests that 

 the first birds might have had all their toes pointing forward, and 

 that the Swifts may have retained this arrangement. But the fact, 

 which he points out, and which I implied in my paper, that this 

 arrangement is not universal even with them, tells against this view, 

 as he admits. As to the embryo, I must say that in some nearly 

 mature embryos of the Common Swift of Europe [Cypselus apns) which 

 I examined, the hallux did not seem to me distinctly directed 

 forwards. 



Besides this, it is noteworthy in this connection that a type of 

 foot with opposable toes is very likely to be developed in consequence 

 of arboreal habits. The Primates almost universally, the Opossums, 

 and Lophiomys in the Rodents, have opposable halluces among the 

 Mammals ; and though the grasping foot of the Chamaeleons is not 

 exactly like that of a perching bird, it shows that a very arboreal 

 reptile can develop a prehensile foot with opposed digits ; and I can 

 see no reason why this should not have taken place with the primitive 

 bird-reptile before it acquired the power of flight. 



III. — By P. Chalmers Mitchell. 



Owing to the opportunities afforded me by the kindness of my 

 friend, Mr. F. E. Beddard, the Zoological Society's Prosector, I 

 have recently been able to devote a considerable amount of attention 

 to the anatomy of the bird's foot, and I am glad to respond to the 

 invitation of the Editor to say something on the interesting discussion 

 raised by Mr. Finn's paper in the June number, and by the editorial 

 note in the July number of Natural Science. 



There are two questions which have an important bearing upon 

 each other, but which must be argued out separately. Mr. Finn 

 argued for his view that three-toed birds, so far as the toes are con- 

 cerned, are degenerate descendants of four-toed birds, and that the 

 avian stock probably arose from an arboreal four- or five-toed reptile. 

 In support of his argument, he brought together the cases in which 

 apparently three-toed birds have been shown to possess a rudimentary 

 fourth toe. In the Natural Scienxe note it was pointed out that 



■* A typical form would be the Jay. Is it not possible that the flight by single 

 violent flaps alternating with sailing often affected by this bird and others similarly 

 winged may represent the earliest form of flight, originating in the effort of a 

 parachuting animal to avoid falling ? 



P 2 



