I OUR GRAY SQUIRRELS 5 
the squirrels scampered, no less to their delight 
than to ours, often leaping one over the other with 
extraordinary agility and grace when two met on 
this single-track, air-line road. 
One of these bridges led to a window-sill in each 
residence, where food was often spread, and it was 
amusing to see the circumspection with which, at 
last, they crept toward it along the icy poles, dig- 
ging their claws into the glazed surface, and often 
slipping astride or almost off the bridge. 
In the tree-tops, where they rush and leap at 
full speed, they are by no means safe from falling, 
but usually manage to catch hold somewhere, often 
by only a single toe, apparently, yet are able to lift 
the body up, like gymnasts, to a firmer foothold. 
Their strength is remarkable, especially in the re- 
gion of the great hams, whose development ac- 
counts for the really astonishing leaping powers 
these animals possess. 
Should they fall clear to the ground, as some- 
times happens, they alight right side up like a cat, 
and seem none the worse for the accident. The 
feet are wide-spread in such a case, and the loose 
skin over the ribs is stretched and flattened out 
very perceptibly. It would seem only a step from 
that condition to the parachute with which the 
flying-squirrel is provided; but if the development 
of this formation in the latter came about through 
natural selection, it must have begun very long 
ago, for Cope has found a fossil (AW/omys), which 
