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AGASSIZ Titicaca" (1875-1876); "Three Cruises of the Blake, a Contribution to American Thalassography" (1880); etc. He died in March, 1910.

AGASSIZ, JEAN LOUIS RODOLPHE, a Swiss naturalist, born at Môtier, Switzerland, May 28, 1807. He studied medicine and comparative anatomy in the universities of Zürich, Heidelberg, and Munich. He gave many years to study of fossil fishes, and his first great work bore that title (1834). His next special researches were directed toward the explanation of glaciers, and he published "Studies of Glaciers" (1844). In 1846 he made a lecturing tour of the United States, and, in 1848, became Professor of Geology at Harvard, and, in 1859, curator of the Museum of Comparative Zoölogy. His contributions to the development of the facts and principles of natural science in his special departments are very numerous and of highest authority. Chief among his works written in English are "Principles of Zoölogy;" "The Structure of Animal Life"; "Scientific Results of a Journey in Brazil"; "Natural. History of the Fresh-Water Fishes of Europe"; and "Contributions to the Natural History of the United States." Other important works are "Studies on the Glaciers," "The Glacial System," and "Researches on Fossil Fishes." He died at Cambridge, Mass., Dec. 14, 1873.

AGATE, a mineral classed by Dana as one of the cryptocrystalline varieties of quartz, some of the other minerals falling under the same category being chalcedony, carnelian, onyx, hornstone, and jasper.

AGAVE, an extensive genus of plants belonging to the natural order amaryllidacæ. The species have large, fleshy leaves, with teeth ending in spinous points. From the center of a circle of these leaves there rises, as the plant approaches maturity, a tall scape of flowers. The idea that the agave blossoms but once in a hundred years is a fable. But as a result of this popular misconception the plant is known under the name of Century Plant. What really happens is, that some species, taking many years (10 to 70, it is thought) to come to maturity, flower but once, and then die. The plant originally belonged to North America and is chiefly found in Mexico. It is now cultivated in the south of Europe.

AGE, any period of time attributed to something as the whole, or part, of its duration: as the age of man, the several ages of the world, the golden age.

In Physiology.—If the word age be used to denote one of the stages of human life, then physiology clearly distinguishes six of these: viz., the periods of infancy, of childhood, of boyhood or girlhood, of adolescence, of manhood or womanhood, and of old age. The period of infancy terminates at 2, when the first dentition is completed; that of childhood at 7 or 8, when the second dentition is finished; that of boyhood or girlhood at the commencement of puberty, in temperate climates from the 14th to the 16th year in the male and from the 12th to the 14th in the female; that of adolescence extends to the 24th year in the male and the 20th in the female; that of manhood or womanhood stretches on till the advent of old age, which comes sooner or later, according to the original strength of the constitution in each individual case, and the habits which have been acquired during life. The precise time of human existence similarly varies.

In Archæology.—The Danish and Swedish antiquaries and naturalists, MM. Nilson, Steenstrup, Forchamber, Thomsen, Worsaae, and others, have divided the period during which man has existed on the earth into three—the age of stone, the age of bronze, and the age of iron. During the first-mentioned of these he is supposed to have had only stone for weapons, etc. Sir John Lubbock divides this into two—the palæolithic, or older, and the neolithic, or newer, stone period. At the commencement of the age of bronze that composite metal became known, and began to be manufactured into weapons and other instruments; while, when the age of iron came in, bronze began gradually to be superseded by the