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ray, in zoology

(Encyclopedia)ray, extremely flat-bodied cartilaginous marine fish, related to the shark. The pectoral fins of most rays are developed into broad, flat, winglike appendages, attached all along the sides of the head...

seal, in zoology

(Encyclopedia)seal, carnivorous aquatic mammal with front and hind feet modified as flippers, or fin-feet. The name seal is sometimes applied broadly to any of the fin-footed mammals, or pinnipeds, including the wa...

Cretaceous period

(Encyclopedia)Cretaceous period krĭtāˈshəs [key], third and last period of the Mesozoic era of geologic time (see Geologic Timescale, tablegeologic timescale, table), lasting from approximately 144 to 65 millio...

ground squirrel

(Encyclopedia)ground squirrel, name applied to certain terrestrial rodents of the squirrel family. In North America the name refers to members of the genus Citellus and sometimes to the closely related genera Tamia...

Lamarck, Jean Baptiste Pierre Antoine de Monet, chevalier de

(Encyclopedia)Lamarck, Jean Baptiste Pierre Antoine de Monet, chevalier de zhäN bätēstˈ pyĕr äNtwänˈdə mônāˈ, shəvälyāˈ də lämärkˈ [key], 1744–1829, French naturalist. He is noted for his stud...

Pauling, Linus Carl

(Encyclopedia)Pauling, Linus Carl pôˈlĭng [key], 1901–94, American chemist, b. Portland, Oreg. He was one of the few recipients of two Nobel Prizes, winning the chemistry award in 1954 and the peace prize in 1...

aging

(Encyclopedia)aging, in biology, cumulative changes in an organism, organ, tissue, or cell leading to a decrease in functional capacity. In humans, aging is associated with degenerative changes in the skin, bones, ...

symmetry

(Encyclopedia)symmetry, generally speaking, a balance or correspondence between various parts of an object; the term symmetry is used both in the arts and in the sciences. In art and design, it is often used in a s...

commando

(Encyclopedia)commando, small, elite military raiding and assault unit or soldier. Although the word was coined in the Boer War (1899–1902), the role is as old as battles themselves. In 1940, when the British org...

Hiroshima

(Encyclopedia)Hiroshima hĭrˌōshēˈmə, hērōˈshmä [key], city, capital of Hiroshima prefectu...