=Ar-chæ-op´ter-yx= [Gr. _archaios_, ancient; _pteryx_, bird.] A fossil bird with reptilian characteristics. =Ar-che-go-sau´rus= [Gr. _archegos_, beginning; _sauros_, lizard.] A carboniferous amphibian (labyrinthodont.) =Ar´go-naut= [Gr. _argo_, swift; _nautes_, sailor.] =Ar-ma-dil´los= [Sp. dim. of _armado_, armed.] Edentate mammals having a carapace formed by ossification of the greater part of the skin and the union of the bony scutes. =Ar-throp´o-da= [Gr. _arthron_, joint; _pous_, foot.] A branch of animals (invertebrates) with jointed legs, as insects, spiders, and crabs. =As´ter= [Gr. _aster_, star.] =As-ter-oi´de-a= [Gr. _aster_, star; _eidos_, form.] Echinoderms having radiating arms with ambulacral grooves below, embracing the true star-fishes. =At´a-vism= [Lat. _atavus_, grandfather.] Reversion; recurrence to an ancestral type. =At´e-les= [Gr. _ateles_, imperfect.] =Au´ri-cles= [Lat. _auricula_, little ear.] A chamber of the heart which receives blood from the veins and transmits it to the ventricle. =A´ves= [Lat. pl. of _avis_, bird.] Birds, a class of vertebrata. =Ba-cil´lus= [Lat. _bacillum_, a little stick.] A genus of bacteria consisting of rod-like cells. They multiply by transverse division and by the formation of endogenous spores. Unicellular plants. =Bac-te´ri-a= [Gr. _bakterion_, stick.] Microscopic unicellular plants. A genus of Schizomycetes (fission-fungi). =Bal-a-no-glos´sus= [Gr. _balanos_, acorn; _glossa_, tongue.] Supposed by some biologists to belong to the Chordata. =Beams= [AS. _beam_, tree.] The main stem of a deer’s antler. =Bel-em´nites= [Gr. _belemnon_, dart.] A belemnitoid cuttlefish. =Bi´o-phores= [Gr. _bios_, life; _phero_, bear.] Biological units of hereditary mass. =Bi´pes= [Lat. _bis_, twice; _pes_, foot.] =Blas´tid= [Gr. _blastos_, sprout.] =Blas-to-ge-net´ic= [Gr. _blastos_, a germ; _genesis_, generation.] Originating in the germ cells. =Blas´tu-la= [Gr. _blastos_, sprout.] A stage in the growth of the embryo; a hollow sphere of one layer of cells enclosing a segmentation-cavity. =Brach-i-op´o-da= [Lat. _brachium_, arm; Gr. _pous_, foot.] Molluscoid animals with bivalve shells, one of which is dorsal and the other ventral; also with brachial appendages coming from the sides of the mouth. Lamp shells. =Brach´i-o-pod= [Vid. Brachiopoda.] Lamp shell. =Bry-oph´y-ta= [Gr. _bryon_, moss; _phyton_, plant.] A division of the vegetable kingdom consisting of liverworts and mosses. =Bry-o-zo´a= [Gr. _bryon_, moss; _zoon_, animal.] Moss animals. =Ca-du-ci-bran-chi-a´ta= [Lat. _caducus_, falling; _branchia_, gills.] Urodeles that lose their gills before maturity. =Ca-du-ci-bran´chi-ates= [Vid. Caducibranchiata.] =Cal´li-thrix= [Gr. _kalos_, beautiful; _thrix_, hair.] =Cal-a-mo-ich´thys= [Gr. _kalamos_, reed; _ichthys_, fish.] =Ca´lyx= [Gr. _kalyx_, cover.] The outermost series of leaves (sepals) of a flower; usually green.