the heart of a long conus arteriosus (anterior to the ventricle) provided with, in many eases, numerous valves, on at least (in Anura) one series at the base, another at the beginning of the truneus where the arches branch off; (2) the strictly symmetrical arrangement of these arches: (3) the three-chambered heart is still like that of Dipnoi; (4) the occurrence of as many as four or even five branchial skeletal arches in the larval stage; (5) the glottis (or entrance to windpipe) is supported by cartilages which themselves are derivatives of posterior visceral arches; (6) the development (in Urodela as in Stegocephalia) of the vertebræ from four pairs of elements called arevalia, and the formation of the intervertebral joints by a split across the intervertebral ring of cartilage; (7) the hypoglossal nerve still lies outside and behind the skull as a cranial nerve; (8) the presence of lateral sense organs; (9) the possession of external gills as in Dipnoi and Crossopterygii. It is frequently assumed that the first Urodela were aquatic creatures, provided with a finned tail and small lungs. Gadow believes these to be larval acquisitions, not ancestral reminiscences. The fact that the ancestors of Amphibia evolved the pentadactyl condition proves that they were land animals. The evolutionary change through which the early Amphibia passes are thus enumerated by Gadow.
(1) "Terrestrial, with two pairs of pentadactyloid limbs; breathing by lungs only; with a fully developed apparatus of five pairs of gill-arches, which during the embryonic life perhaps still carried internal gills, with or without several pairs of gill clefts. Reduction of the dermal armor and of the cutaneous scutes had taken place.
(2) "Additional respiratory organs were developed by the embryo, in the shape of external gills; these were at first restricted to embryonic life (as in the existing Apoda), but were gradually used also during the aquatic life of the larva. These external gills, together with the lungs, have superseded the internal gills, of which there are now no traces either in Urodela or in Anura.
(3) "Some Urodela, retaking to aquatic life, retained and further enlarged the external gills into more or less permanent organs. The majority of Urodela hurried through the larval, aquatic stage, and some — e.g., Salamandra atra — became absolutely terrestrial. The possession of unusually long external gills by this species and by the Apoda indicates that these organs are essentially embryonic, not larval, features."
Bibliography: the foremost systematic writers upon this group are G. A. Boulenger, of the British Museum, and E. D. Cope. The latter has completely monographed North American forms in "Batrachia of North America," Bulletin 34, United States National Museum (Washington, 1889). This discusses the larger relations of the group, and gives an extensive bibliography. For a still more recent general treatise, consult H. Gadow, "Amphibia," Cambridge Natural History, Volume VIII. (Cambridge. 1901). See Alimentary System (Evolution of) and similar articles relating to comparative anatomy.
AMPHIBIA, Fossil,. See Stegocephalia.
AMPHIB'IOUS PLANTS. A remarkably plastic group, generally classed among water plants (Hydrophytes, q.v.). Not only are these plants able to endure life in wet or dry habitats, but their leaves often show remarkable variations. (See Leaf.) Shallow ditches commonly furnish good illustrations of amphibious plants.
AM'PHIBOLE (Gk. ἀμφίβολος, amphibolos, doubtful, ambiguous; alluding to its being easily confounded with augite). An important group of rock-making minerals closely allied to the Pyroxene (q.v.) group. The amphiboles are metasilicates, principally of calcium, magnesium, or iron, and sometimes also of manganese, sodium, and potassium. The group is subdivided according to the forms of crystallization. Those that crystallize in the orthorhombic system include Anthophyllite and its variety Gedrite; the monoclinic section includes the typical mineral Amphibole with its varieties, as well as Glaucophane, Crocidolite, and certain other minerals; while the triclinic section includes Ænigmatite. All of these minerals have a common prismatic cleavage of from 54° to 56°, and also agree in their optical characters and chemical composition.
The most important member of the group is the mineral Amphibole, which gives its name to the series. The several varieties of amphibole are divided into two groups, according as they do or do not contain aluminum. The non-aluminous varieties include Tremolite, a calcium magnesium silicate that is usually white to dark gray in color, and is found both in crystals and massive; Actinolite, a calcium magnesium and iron silicate of varying shades of green; Grünerite, an iron silicate which is of a brown color that occurs in fibrous masses. The aluminous varieties include the several varieties of Hornblende, which comprises the dark green and black varieties, known as common Hornblende (black), Pargasite (green and blue), and Edenite (white, gray, and pale green). These minerals are found in crystalline metamorphic limestones, granitic, and schistose rocks, and in volcanic or igneous rocks. Nearly every member of the group has several varieties, each of which, besides having a separate name, differs from the type by some slight variation in color, optical properties, or chemical composition. Many varieties of amphibole have been cut as gem-stones.
AMPHIC'TYON'IC COUN'CIL (from Amphictyon; see below). A celebrated religious congress of the confederated tribes of ancient Greece, which met twice every year, in spring and in autumn, at both Delphi and Thermopylæ. The meetings at Delphi took place in the temple of Apollo, those at Thermopylæ in the temple of Demeter, which was in the village of Anthela. The congress was composed of the deputies of twelve tribes, the list of which is given differently in different authors. The list of the orator Æschines (containing but eleven names, however) is as follows: Thessalians, Bœotians, Dorians, Ionians, Perrhæbians, Magnetes, Locrians, Œtæans, Phthiots, Malians, and Phocians. The twelfth tribe was probably either the Dolopians or the Ænianians. (See Pausanias. ix. S. and Herodotus, vii: 132: also Cauer in Pauly-Wissow's Realencyclopädie). Each tribe sent two members, and the twenty-four representatives possessed equal authority. The origin of the Amphictyonic Council is a matter of legend only. Tradition connects it with the name of Amphictyon, son of Deucalion, or with that of
