OPOSSUM, the name of sev eral American marsupials, also applied in Australia to the phal angers (q.v.). True opossums are found almost throughout America (see MARSUPIALIA). They form the family Didelphyidae,. dis tinguished by the opposable first hind-toe and by the dentition. They are small, nocturnal animals, with long noses, ears and tails, the latter being usually naked and prehensile. The opposable first hind-toe is clawless and the tip is expanded into a flat pad. The other digits all bear claws. Mainly arboreal, they feed on birds, insects and fruit. The best known species of the type-genus is Didelphys virginiana, which is very common in the United States. It is nearly the size of a cat, grey in colour, the fur being woolly. When caught, it feigns death (hence the expression "playing 'possum"). The ova of opossums have a thin horny shell, and many more are produced than can survive. The female produces 6 to 16 young, after a period of gestation of 14 to 17 days. At birth the immature and helpless young, only about in. long, are placed by the mother
in her pouch, where they cling to the nipples by their mouths. When big enough to leave the pouch, the young are often carried on the mother's back, holding on to her fur or clinging to her tail by their own prehensile tails.