SCIUROPTERUS VOLUCELLA. 
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energy of their movements at first, they usually increase in vigor 
and speed until after midnight and scarcely grow less before morn- 
ing. Nothing affords them so much gratification as a large wheel 
which is placed inside the cage. Into this wheel they jump when- 
ever aught disturbs or pleases them, and even when quite hungry 
they often find it necessary to take a few turns before commencing 
their meal, after which exercise they draw themselves into a bunch 
with the tail over the back, after the manner of squirrels, and set 
briskly to work on the nut or other food they may have 
received. They are almost as fond of riding as of running, and 
work their passage by running till the wheel is in rapid motion and 
then clinging to its wires, and so are carried around and around, 
the pure white of the under side of the body contrasting prettily 
with the soft brownish-gray of the back and sides as each comes 
into view. When both are in the wheel one often rides while the 
other turns the wheel, the latter bounding over the other as each 
turn brings him around, and, no matter how rapidly the wheel 
turns, these movements are executed with perfect exactness and 
gracefulness. Being desirous of knowing with some degree of 
accuracy how rapidly the wheel moved, I made some experiments 
for that purpose and found that the usual rate of revolution was 
from sixty to over a hundred and twenty times a minute, and, as 
the wheel is forty-four inches in circumference, when its rate is the 
latter of the two numbers named, the squirrel turning it must 
travel four hundred and forty feet a minute, or about five miles an 
hour, a distance requiring a great many steps when they are 
so short as squirrels must take. The sides of the wheels are formed 
of spokes radiating as in any wheel, these spokes are only five 
inches apart at the circumference and of course constantly grow 
less toward the centre ; yet through this narrow space which passes, 
when the wheel is at full speed, in the sixteenth of a second, they 
dart in and out with perfect ease. So quickly do they move that 
the eye can scarcely follow them ; one instant a squirrel is in the 
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