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brain

(Encyclopedia)CE5 Brain brain, the supervisory center of the nervous system in all vertebrates. It also serves as the site of emotions, memory, self-awareness, and thought. Brain research, now often referred ...

menstruation

(Encyclopedia)menstruation, periodic flow of blood and cells from the lining of the uterus in humans and most other primates, occurring about every 28 days in women. Menstruation commences at puberty (usually betwe...

spider

(Encyclopedia)spider, organism, mostly terrestrial, of the class Arachnida, order Araneae, with four pairs of legs and a two-part body consisting of a cephalothorax, or prosoma, and an unsegmented abdomen, or opist...

barnacle

(Encyclopedia)barnacle, common name of the sedentary crustacean animals constituting the infraclass Cirripedia. Barnacles are exclusively marine and are quite unlike any other crustacean because of the permanently ...

sex

(Encyclopedia)sex, term used to refer both to the two groups distinguished as males and females, and to the anatomical and physiological characteristics associated with maleness and femaleness. Sex relates to the t...

elephant

(Encyclopedia)elephant, largest living land mammal, found in tropical regions of Africa and Asia. Elephants have massive bodies and heads, thick, pillarlike legs, and broad, short padded feet, with toes bearing hea...

migration of animals

(Encyclopedia)migration of animals, movements of animals in large numbers from one place to another. In modern usage the term is usually restricted to regular, periodic movements of populations away from and back t...

transplantation, medical

(Encyclopedia)transplantation, medical, surgical procedure by which a tissue or organ is removed and replaced by a corresponding part, usually from another part of the body or from another individual. A life-saving...

Mollusca

(Encyclopedia)Mollusca məlŭsˈkə [key], taxonomic name for the one of the largest phyla of invertebrate animals (Arthropoda is the largest) comprising more than 50,000 living mollusk species and about 35,000 fos...

vitamin

(Encyclopedia)vitamin, group of organic substances that are required in the diet of humans and animals for normal growth, maintenance of life, and normal reproduction. Vitamins act as catalysts; very often either t...