1881.] 
308 
[Jeffries. 
swamp, marsh and water birds, on the end of the first finger, and 
are only found on the end of the second finger among the Ratitae 
and Palamedea. Here Nitzsch made a mistake by confounding 
the spurs of Palamedea with true claws. Judging from quo- 
ations the editor of the Fredrius works distinguished between 
claws and spurs ; these works, however, I have not been able to 
procure. The error made by Nitszch is repeated by Selenka 
who does not distinguish between spurs and claws. 
The claw proper is found on the end of the first finger of very 
many birds, and much more rarely on the end of the second finger. 
In both cases the claw invests the last phalanx of the finger. 
A claw, in the case of the thumb is almost always, if not always, 
present when a second phalanx exists. This is not the case with 
the second finger, since many birds have three phalanges but no 
claw in this finger; when a claw is present, however, a third phal- 
anx also exists. That is, the claws always have ungual phalanges 
which correspond to the last joints of our thumb and second 
finger. 
The claws are developed in just the same way as the spurs, and 
differ only in that the one is a simple horn on the edge of the 
wing while the other is a horny case surrounding an ungual 
phalanx. That this like development does not show any close 
affinity is shown by the origin of all horn from this layer. The 
horn of the claws, spurs, scales, feathers, beak and papillae of 
the tongue all come from this layer. Mesodermal structures, horn- 
like in nature; may be afterwards developed within modified pap- 
illae, but never, so far as I know, consist of horny fusiform cells. 
That these smooth, inconspicuous claws have no special use in 
the life of modern birds, must be clear to all who examine their 
relations to the strong quills of the wing feathers. Accord- 
ingly, we are forced to consider them the result of inheritance 
from some ancestors where they were of use, that is as aborted 
organs. With this consideration in mind when studying the num- 
ber of primaries, where it is necessary to determine accurately 
the tip of the second finger, I looked and found the rudiments of 
one in the embryo of the tame duck, some water birds, and appar- 
ently also in a hawk. The hawk I was unable to make sections 
of, and so could not positively prove the existence of the claw. 
