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 and Pollux Castor (Alpha Geminorum) and Pollux (Beta Geminorum). As emblems of immortality and death, the Dioscuri, like Heracles, were said to have been initiated into the Eleusinian mysteries. Castor and Pollux are consistently associated with horses in art and literature. They are widely depicted as helmeted horsemen carrying spears. The Pseudo-Oppian manuscript depicts the brothers hunting, both on horseback and on foot. On votive reliefs they are depicted with a variety of symbols representing the concept of twinhood, such as the "dokana" (δόκανα – two upright pieces of wood connected by two cross-beams), a pair of amphorae, a pair of shields,