MEET ee 
Sa a i a 
1894.] Development of the Wing of Sterna wilsonii. 771 
but that there must be (at least one) digits buried beneath the 
feathers, and in just the place where the missing finger or fingers 
should come is an evident ridge in the stone. 
If we may call upon the effects of use and disuse, the con- 
ditions presented would also tend to favor the reduction of the 
digits on the radial side, for it is the ulnar phalanges which 
must bear the stress of the wing; the fingers on the radial 
side, having but few small feathers, would be most likely to 
disappear. 
Jeffries invokes also the distribution of the nerves, but to 
my mind his evidence is not conclusive; besides it is directly 
negatived by the distribution of the blood vessels as was 
pointed out above. 
We may conclude, then, that the only conditions possible 
are either I, II and III, or II, III and IV, and that until some 
evidence be found of the actual appearance of a fifth digit on 
the ulnar side, that there is at least as much reason for the 
second as for the first formula. In regard to the first, Hurst 
remarks, it “isin no ease, so far as I am aware, supported by 
any evidence whatever. I believe it to have originated from 
the pre-Darwinian statement that the Ala spuria is ‘ analo- 
gous to the thumb; while the other two digits are called 
simply ‘second’ and ‘third ; that is, second and third digits 
not of the pentadactyle but of the tridactyle fore-limb. Such 
phrases written on the then undoubted hypothesis of special 
creation and of fixity of species, could obviously not mean 
that the three digits called ‘thumb’ and ‘ second’ and ‘ third’ 
had been evolved from the digits T, IT, III of the pentadactyle 
fore-limb of an ancestor; the author did not believe that 
birds ever had such an ancestor. The transcription of such 
phrases into post-Darwinian treatises, without consideration of 
the new meaning which they would thus gain from the new 
context, appears to have been the origin of the error." 
CONCLUSIONS. 
Carpats. There are at least seven elements in the carpus. 
In the proximal row there are two free elements (intermedio- 
radiale and centralo-ulnare) both of which are divided in the 
