North American beaver large, webbed hind feet. The unwebbed front paws are smaller, with claws. The eyes are covered by a nictitating membrane which allows the beaver to see under water. The nostrils and ears are sealed while submerged. A thick layer of fat under its skin insulates the beaver from its coldwater environment. The beaver's fur consists of long, coarse outer hairs and short, fine inner hairs (see Double coat). The fur has a range of colors, but usually is dark brown. Scent glands near the genitals secrete an oily substance known as castoreum, which the beaver uses to waterproof its fur.
Castor Oyl prominent appearance in the series is as a member of Popeye's orchestra in the 1935 short "The Spinach Overture". In the 1980 film directed by Robert Altman, Castor is a key character, and is played by actor Donovan Scott. In the film, however, he is made Olive's younger brother and is considerably less sophisticated than his comic strip counterpart. Castor Oyl is named after castor oil, a medicine often given to children for various ailments until the mid 20th century. His mother Nana's name derives from "banana oil," an epithet similar to "baloney." His father Cole's name derives from "coal