1894.] Development of the Wing of Sterna wilsonii. 765 
Srace VII, (Fro. 7). 
There is little in this stage(fig. g) to note except metacarpal 
V. This is now an oval disk closely applied to the ulnar 
flexor surface of metacarpal IV, about one-ninth of the dis- 
tance from the proximal to the distal end. It no doubt finally 
unites with metacarpal IV at that point. 
COMPARISONS. 
INTERMEDIO-RADIALE. In Sterna in the earlier stages these 
two elements are distinct (fig. 1); later they become so com- 
pletely fused that they cannot be distinguished, although, 
exceptionally, (fig. 4) they partially retain their individuality 
for a considerable time. Similar conditions have been noted 
in several birds, e. g., Opisthocomus, Fulco tinnunculus and 
chick by Parker and Cypselus melba by Zehntner (90). In 
other birds the separation has not been described, possibly 
from the fact that the proper stages have not been studied. 
ULNARE-CENTRALE. My observations here closely agree 
with those of Parker on the ducks and auks, there being the 
same tendency to subdivision of the cartilage mass into two 
elements which he shows. One of these is, beyond doubt the 
ulnare, but I confess I am not so certain of the other which I 
call centrale in deference to his better opinions. The condi- 
tions shown in fig. 1 where the two portions of this element 
are clearly shown, leads one to the conclusion that the distal 
lobe may possibly belong to the series of carpales, in which 
case it would be that of the fourth existing digit. In fig. 5 
again the arrangement is such as to support such a view, 
while on the other hand, in none of the earlier specimens 
have I seen it in such a position as to indicate that it should 
be regarded as a centrale. In Chloéphaga poliocephala Parker 
(90) describes this bone as divided into three portions, the two 
distal of which he terms centrale 1 and 2. It would rather 
seem as if we had here to do with a true centrale, while Park- 
er’s centrale 1—clearly, according to position, equivalent to 
the single one which I find—must be regarded as a fourth 
carpal. (Cf. Parker '90, pl. 5, fig.14). Studer, according to the 
