290 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1949 
not to be disturbed by the swinging of the bag, which perhaps simu- 
lates the swaying of the trees in which they would normally live. 
They are, however, distinctly disturbed by vibration produced by 
rubbing the door or the rod on which the bag hangs, which would 
probably remind them of the disturbance made by an enemy climbing 
to their nest in a tree. When thus awakened, they usually react in 
one of two different ways. If sharply startled they are very likely to 
dash out of the nest ready to take off in a glide or run to another, safer 
location; or if the alarm is not so sudden they may merely quickly 
and quietly go to the entrance of the nest and look out to see the 
cause of the disturbance. This behavior is, of course, associated with 
the rather exposed location in which they live, where danger may 
arrive from almost any direction and their best chance for survival 
may be to flee. 
I am inclined to think that the African elephant shrews (Macrosce- 
lides rufescens) sleep with both eyes open instead of only one. I 
have kept some in my den to study them at all hours of the day and 
night, and I have yet to see them with their eyes closed. They are 
invariably sitting upright with their eyes wide open, or at most only 
slightly closed. This trait suggests that they probably sit above 
ground in more or less exposed locations and are perpetually alert 
for danger. 
A wide variety of poses are assumed by animals in sleeping. In 
addition to the well-known attitudes of lying on the ventral surface, 
the back, or the side, a great many curl up in a very compact ball. 
The squirrels and others with bushy tails tuck the head and feet well 
inside and wrap the tail around them so that it actually affords some 
protection and warmth for the back of their necks and their backs. 
In this curled-up position they may lie on the side, but more frequently 
the head and feet are on the underside with the top of the head actually 
resting on the surfaces on which they are sleeping. This is a common 
position among a great many of the rodents. The giant anteater lies 
on its side, curls its head and feet together, and covers itself with 
its very long-haired tail which serves as a blanket and, perhaps in 
the wild, to some extent as camouflage. The sloths sleep hanging 
beneath a limb with the head thrown upward and forward so that it 
rests on the chest, or they may be partially sitting in the fork of a 
tree with the head forward between the upper arms, the tree trunk, 
and the chest. Some animals sleep standing up. Horses commonly 
do this, and some elephants do much of their sleeping standing. 
Most of the bats sleep hanging head downward, being suspended by 
the nails of their hind feet. The red bat (Nycteris), which sleeps 
hanging on a twig in a tree, has an extensive membrane between the 
hind legs which it draws downward so that it serves as a protection 
to the ventral parts of the body. When hanging head downward, 
