SOME RESULTS OF OSTRICH INVESTIGATIONS. 2/5 



sequence — total loss of the shaft, loss of barbules, loss of barbs. 

 Even the larger contoiu^ feathers appear not to drop out as a 

 whole, but in a definite piecemeal fashion. 



Third Digit of Wing. 



In all living birds the third digit is greatly reduced, and 

 buried in the muscles of the wing. This is usually the case in 

 the adult ostrich, though its outline can be distinctly felt through 

 the thin skin. In the embryo, however, the finger is clearly seen 

 at about the tenth day of incubation, and is then of equal size 

 with the second, which is by far the largest of the thre§ in the 

 mature wing. From the tenth day onwards the second digit 

 greatly outstrips the third in growth, and within a few days of 

 hatching the latter shows as a small triangular projection from 

 the post-axial border of the wings, much larger in some embryos 

 than in others. After hatching, the projection generally dis- 

 appears, and no trace is to be seen from the exterior. Dissections 

 show that the first phalanx is always well developed, but the 

 second is usually represented by only a very small nodule, of 

 bone. The first and second fingers bear well-defined claws, and 

 some writers assert that a claw appears on the third also,* but 

 this has never been found in the hundreds of birds coming under 

 my observation, although specially looked for. 



While the third digit is usually hidden, as above described, 

 on some birds it forms a distinct projection from the general 

 imder surface of the wing, and may even extend beyond the 

 border in a finger-like manner. (PI. 50.) All intermediate 

 stages between the extremes are to be met with on the large 

 number of birds examined. Owing to the manner in which the 

 bird drags its wings over the ground when taking a "' sand bath," 

 the projecting finger comes in for a good deal of rough wear on 

 the hard ground, and develops a knob-like callosity as a response. 

 In birds with the finger projecting conspicuously, the second 

 phalanx is a bone nearly an inch in length, instead of a mere 

 nodule, and its free end becomes knob-like in correlation with 

 the callosity ; but all intermediate stages in the size of the phalanx 

 can be procured. 



Among the number of adult ostriches available for study, 

 we therefore find numerous stages which serve to illustrate the 

 manner in which the degeneration of the third digit is proceeding, 

 and these are supj)lemented by the embryonic stages. Externall\ 

 there may be no trace of the digit, while again it may project as a 

 distinct finger, callous at the tij) ; also the second or terminal 

 phalanx may be represented l)y stages from a mere nodule to a 

 bone an inch or. so in length. Difl:'erent individuals have reached 

 dififerent .Sitages in the degeneration of the digit, but they reveal 

 that the passage from one to the other is by imperceptible 

 degrees, not by conspicuous steps. The genetic factors concerned 



* Parker and Haswell : 'Text-Book of Zoology. 11. ,^9J. 



