1891. ] NEW YORK ACADEMY OF SCIENCES. 31 
nected mechanically, in an interesting manner, with the extremity 
of the upper mandible—along the cavity of this mandible. 
The fact that immediately after the death of the bird, when the 
bill is in its flexible condition, this opening of the bill, at its ex- 
tremity, may be accomplished by any one who knows how to pro- 
duce the proper action of the muscles, was discovered by Mr. C. C. 
Trowbridge about two years ago, while examining specimens of the 
Hudsonian godwit that he had shot. An examination of the 
woodcock by him showed similar action. 
The solution of the object of the flexibility of the upper mandi- 
ble at its extremity, connected with the fact that the opening of the 
bill at the end (as in sketch No. 2) is under the control of the bird, 
is doubtless as follows : 
When the bill is forced into soft ground it must be closed to its 
very extremity ; it then acts like anawl. To open the bill and seize 
an object reached, if both mandibles were hard and inflexible through- 
out their whole length it would be necessary for the bird to enlarge 
the hole around its bill along its whole extent ; an operation requiring 
much force, and possibly the opening and closing would be in such 
case impracticable. But the opening at the extremity to the slight" 
extent necessary to take in its food is comparatively a simple mat- 
ter. Moreover, when the food is seized and the bill withdrawn 
through the small hole made by the bill the effect during the whole 
of the withdrawal of the bill is to cause the food to be clasped more 
firmly and securely. The operation of withdrawing the food would 
otherwise be very difficult, and possibly impracticable. 
Professor Trowbridge also presented the results of some further 
observations made by Mr. C. C. Trowbridge, on the locking or 
overlapping of the primary wing feathers by certain birds during 
flight. 
Attention was called to the fact that about four years ago (Oct. 
17, 1887) he had read a paper before the Academy describing this 
locking of the primaries of certain hawks, discovered by Mr. C. C. 
Trowbridge, and stated that, as the number of specimens then ex- 
amined was small, and although the fact of this habitual locking or 
overlapping, especially during soaring flight, seemed completely 
established for certain hawks; yet from time to time observations 
had been continued; a most remarkable opportunity for such. ob- 
servations having occurred this autumn during the month of 
September. 
Large flights of hawks migrating southerly took place near New 
Haven on the 8th, 9th, and 14th of. September. On those days the 
wind was northerly and high, and advantage was taken, for the 
purpose of procuring specimens, of a high hill around which hawks 
and eagles were circling. Large numbers passed within shooting 
distance, generally soaring, but frequently soaring and flapping 
alternately. 
On September 8th nine hawks were shot, on September 9th 
three, on September 14th fourteen, in all twenty-six, embracing 
