See AIDS.参阅18页AIDS。...[继续阅读]

    Any chordate animal with a noto-chord and lacking a brain and skull. Acrani-ates include the urochordates and cephalochor-dates. See Cephalochordata,Urochordata.指任何脊索动物中具有脊索而缺乏大脑和头骨的动物。无头骨类包括尾索动物和头索动物。参阅142页 Cephalo...[继续阅读]

    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...[继续阅读]

    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 ...[继续阅读]

    See corticotropin.参阅203页corticotropin。...[继续阅读]

    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...[继续阅读]

    See radial symmetry.参阅693页radialsymmetry。...[继续阅读]

    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...[继续阅读]

    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 一类,其木质部呈星形、韧皮部位于星状木质部之间。参阅778页stele。...[继续阅读]

    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...[继续阅读]