See AIDS.參閱18頁AIDS。...[繼續(xù)閱讀]

    Any chordate animal with a noto-chord and lacking a brain and skull. Acrani-ates include the urochordates and cephalochor-dates. See Cephalochordata,Urochordata.指任何脊索動物中具有脊索而缺乏大腦和頭骨的動物。無頭骨類包括尾索動物和頭索動物。參閱142頁 Cephalo...[繼續(xù)閱讀]

    Developing from the base upwardsso that the youngest structures are at the apex.An acropetal sequence of development is seenin flower formation in which the calyx formsfirst and the carpels form last. The term mayalso be applied to the movement of substan...[繼續(xù)閱讀]

    A membrane-bound structure inthe anterior head region of a spermatozoon,usually forming a cap over the nucleus. Itcontains enzymes that are released on contactwith the egg at fertilization and break downthe egg coats,enabling the spermatozoon nu-cleus to ...[繼續(xù)閱讀]

    See corticotropin.參閱203頁corticotropin。...[繼續(xù)閱讀]

    One of the two contractile proteinspresent in muscle. Actin molecules are capa-ble of polymerization to form the thin fila-ments that are part of the muscle myofibrils.Thus muscle myofibrils consist of alternatingand overlapping sets of thick myosin and t...[繼續(xù)閱讀]

    See radial symmetry.參閱693頁radialsymmetry。...[繼續(xù)閱讀]

    Agroup of bacteria characterized by a mycelialfungus-like growth habit and belonging to thephylum Actinobacteria. They are numerousin the topsoil and are important in soil fertili-ty. Some may cause infections in animals andhumans. Most of the antibiotics...[繼續(xù)閱讀]

    A type of protostele in whichthe xylem is star shaped and the phloem liesbetween the points of the star. See stele.原生中柱的 一類,其木質(zhì)部呈星形、韌皮部位于星狀木質(zhì)部之間。參閱778頁stele。...[繼續(xù)閱讀]

    The transitory change inelectrical potential that occurs across themembrane of a nerve or muscle fiber duringthe passage of a nervous impulse. The degreeof change is independent of the strength ofthe impulse;it either occurs or does not (seeall-or-none).I...[繼續(xù)閱讀]