Flying Squirrel
2 of the 6 encyclopedias on this shelf carry an entry for Flying Squirrel. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
a squirrel-like animal provided with a loose fold of skin on each side of the body. When the animal leaps it spreads out its legs to their full extent, the fold which runs from fore leg to hind leg is stretched out into a sort of a flying machine . "It opens its vestments, leaps into the air, and sails down the steep incline from the top of one tree to the foot of the next as lightly as a bird." As it nears the end of its slide or flight it gives a graceful upward turn, partly to light head uppermost and partly to check its speed. Properly speaking, it cannot fly, but it can use its momentum to slide upward and can change its course. If it is desirous to continue its journey it runs up the trunk of a tree to a lofty outlying limb, and launches out into midair again. The flying squirrel is active in the twilight hours. It has soft, delicate, noiseless fur. It is a timid, gentle animal, feeding on much the same food as its larger red relative. A number of small species are found in Europe and in North America . A very similar group inhabits the forests of southern Asia.
Collier's New Encyclopedia (1921)
a name given to such of the Sciurida (squirrels) as have the skin of the sides very much extended between the fore and hind legs, so as, to a certain extent, to sustain the animal in the air when taking long leaps. Sciuopterus volans is the only European species.
What Has Changed in the Last Century
The mechanics described in Aiton's 1910 entry are essentially right: flying squirrels glide rather than fly, on a skin membrane (the patagium) stretched between fore and hind limbs, and they do pitch up at the end of a glide to brake and land head-uppermost. Modern work has added the details aft cartilage spur on the wrist that spreads and steers the membrane, glides measured at 45 metres and more, and a tail used as an air brake aft and has counted about 50 species in the tribe Pteromyini, most of them Asian rather than European or American. Collier's 1921 note that one species is European still holds, though it is now called Pteromys volans, the Siberian flying squirrel, and in Finland and Estonia it is a protected animal in decline. Two newer surprises: a third North American species, Humboldt's flying squirrel, was separated out in 2017, and in 2019 researchers reported that North American flying squirrels fluoresce bubblegum pink under ultraviolet light.
Written for this edition, 2026.