IV. 



Biological Theories. 



VII.— THE DIGITS IN A BIRD'S WING: A STUDY OF 

 THE ORIGIN AND MULTIPLICATION OF ERRORS. 



THE plate accompanying this essay is a photograph from nature of 

 the dorsal aspect of the left wing of the specimen of Avchceopteryx, 

 which is now in the Museum of the Berlin University, and which was 

 found, in 1S77, in a stratum belonging to the Upper Jurassic series, 

 near Eichstatt in Bavaria. This photograph is now published because 

 the best known figure of this specimen is characterised not so much by 

 carelessness or by inadvertent error as by wilful falsification. That 

 figure has, however, been copied into some of the best palaeonto- 

 logical and geological treatises, and has received the authoritative 

 sanction which insertion in Zittel's " Palaeontologie " involves. In 

 controverting views supported by such an authority, and views to 

 be found even in the careful writings of Professor Huxley, and of 

 almost every lesser light who has ever expressed an opinion on the 

 subject, it is hardly probable that I should gain credence if I had 

 given merely a new drawing. The photograph, however, will carry 

 conviction. 



In the plate, the humerus, the straight radius, and curved ulna, a 

 carpal bone, and three long slender fingers may be seen at a glance. 

 The fingers are all clawed, though the claw itself is not easy to 

 make out : still the form of the ungual phalanx can leave no doubt 

 upon the subject. 



The fingers are recognised by everybody as being the equivalents 

 (or homologues) of the digits I, II, and III of the normal 

 pentadactyle sauropsidan fore-limb : this view is fully supported by 

 the relative positions of the three fingers and by the numbers of 

 phalanges — two, three, and four respectively — which they possess. 



To the post-axial side (left in the plate) of the ulna and of the 

 fingers is seen a wing in a marvellously perfect state of preservation. 

 In the original, even the barbules of some of the quills are recognisable, 

 and the barbs are easily seen even in the photograph. Of. the quills, 

 there are sixteen or seventeen (possibly even one more). The 

 seven are primary quills, and these are of chief importance to us for 

 the present purpose. To merely state that the fourth is straight, 



t 2 



