654 General Notes. [July, 
which is to deny the equality of the forces producing the 
balance. 
Bear in mind that I have carefully excluded inertia, or in other 
words, mass acceleration, from the problem. The birds have the 
power of flapping, or falling from higher to lower levels, to initiate 
their movements. Soaring has nothing to do with acceleration. 
It deals with motions of uniformity only. Hence I am justified 
in holding that one or two pounds of constant pressure is compe- 
tent to drive the plane edgeways 1000 feet per second against air 
friction only. As frictional air resistance approaches zero, a small 
force would move the plane against it with great velocity. No 
weight is lifted in the upward motion, as the forces producing the 
weight are already employed to their total value, as fully shown. 
s the force producing the lateral motion is derived from the 
gravity of the mass, I am also justified in holding that a soaring 
bird is trafislated at right angles to the gravitating force, or hori- 
zontally, solely by the action of that force. It will be noticed that 
forces were on hand in quantity sufficient to produce the 
movement.—/. Lancaster, Chicago, Til., June 5th, 1886. 
LimuLus IN THE PaciFic.—My friend, Mr. H. W. Turner, of 
the U. S. Geological Survey, sends me an extract from the San 
the Atlantic coast. It is thought that the crab must have $ 
hatched from eggs brought with the lobsters which were li 
ated in these waters seven or eight years ago: —S. L. [Can 
have been the Japanese species >—Ep.] 
’ 
THE SwIM-BLADDER OF FisHEs.—Charles Morris has publishes 
in the Proceedings of the Philadelphia Academy, a theory 0r: 
origins of lungs and swim-bladder, and an explanation o 
_ homologies and the peculiarities of their relative positions. 
imagines that the primitive fishes, like the sharks, wer 
this organ, but that some of them, venturing on | 
or shorter excursions, took in stomach and th 
which procured a certain aération of the blood. es of its 
e 
_ that the air held in the throat finally produced a dite it later 
_ @ sae with a narrowed opening. The tendency to Tise Yo. 
in the water would ensure that this bag of air should maintain? : 
ee a 
= without 
and for ee 
oatfuls of ais 
r s 
e. 
-superior wall, which became later a diverticulum and | A . 
