TTHHEE NNEEWW PPEENNGGUUIINN DDllCCTTll66NNAARRYYOOFF LL OO GG YY ,,-- MM.. AAbbeerrccrroommbbiiee MM.. HHiicckkmmaann MM.. LL.. JJoohhnnssoonn MM.. TThhaaiinn 00 EEIIGGHHTTHH EEDDIITTIIOONN II - I I PENGUIN BOOKS :: F PENGUIN BOOKS i Published by the Penguin Group Penguin Books Ltd, 27 Wrights Lane, London W8 5TZ, England Penguin Books USA Inc., 375 Hudson Street, New York, New York 10014, USA I Penguin Books Australia Ltd, Ringwood, Victoria, Australia Penguin Books Canada Ltd, 2801 John Street; Markham, Ontario, Canada L3R 1 B4 j T Penguin Books (NZ) Ltd, 182-190 Wairau Road, Auckland 10, New Zealand Penguin Books Ltd, Registered Qffices: Harmondsworth, Middlesex, England s First published as The Penguin Dictionary of Biology, 1951 Second edition 1954 ’ Third edition 1957 ’ Fourth edition 1961 Fifth edition 1966 Sixth edition 1973 Seventh edition 1980 Eighth edition, entiRed The New penguin Dictionary of Biology, 1990 3579108642 Copyright 0 M. Abercrombie, C. J. Hickman and M. L. Johnson, 1951,1954, 1957, 1961, 1966,1973, 1980 Copyright 0 Michael Thain, the Estate of M. Abercrombie, the Estate of C. J. Hickman and the Estate of M. L. Johnson, 1990 All rights reserved The acknowledgements on pages ix-x constitute an extension of this copyright page Printed in England by Clays Ltd, St Ives plc Filmset in 9 on lO+pt Monophoto Times m Except in the United States of America, this book is sold subject to the condition that it shall not, by way of trade or otherwise, be lent, re-sold, hired out, or otherwise circulated P’ without the publisher’s prior consent in any form of I_- binding or cover other than that in which it is L published and without a similar condition including this condition being imposed IF” on the subsequent purchaser I %+a .__-_i ,._-_ __-”__ .....--..- _ __,-- ?_ __ _____^I_I_ _II - ..~.__ -se%4 P FOR KATEY AND AVRIL, AND MARGARET / h .- PREFACE TO EIGHTH EDITION In the first major revision of this work for some years, changes were overdue to both its form and content if we were to ensure its continu- ance as a valuable reference book for school and undergraduate work. While remaining within the tradition set by the previous authors, we I provide more of the encyclopaedic type of entry, in particular for terms : central to theory and for those describing a phenomenon or process ; central to much else in the discipline. These articles and the extensive 1 cross-referencing of most entries will not please everyone, least of all those who consult this dictionary merely as a lexicon. For brevity’s i sake we have dispensed with many definite and indefinite articles, but 1 have tried to keep the result grammatical. F: It may be argued against us that some head words rarely turn up in . E the literature. In defence, terms such as arms race and cost of meiosis are included here not because they are particularly common in the literature but because they represent convenient headings under which to include important material that would have been difficult to place [ elsewhere without over-stretching another entry. In a few cases, indeed F on the very first page, several entries with a mutual bearing on one another have been brought together under a single head word or phrase, we hope for interest as well as convenience. Where this occurs, all included subterms are separately listed, directing the reader to larger entries. Terms in small capitals indicate where the reader might choose to pursue related matters raised by an entry; for a cross-referencing role lies firmly in this dictionary’s tradition. Some will argue that this detracts from what little aesthetic appeal the work may have; but cross- I references frequently provide information which it was the authors’ - hope should be read, although by no means all terms with separate entries are given small capitals. Italicized terms either indicate subdivis- ions of an entry or those terms with a particular tendency to be found associated with the head word. Others have less explicit claim to emphasis, but were simply considered worth stressing. We have endeavoured throughout to include genuinely informative material, in addition to stating -the obvious. Advanced readers will share with us the common frustration of finding too little interesting information in dictionary entries, and we have sought to avoid that. Each entry could have been written in many ways, and although we have never knowingly side-stepped the thorny problems that many attempts at definition pose, we must often have oversimplified through ignorance. However, it did not seem possible to do justice to such terms as gene, classification and species, without including some of the philoso- phical issues they raise. Likewise, it seemed at times inappropriate to exclude a little historical information. To this extent we hope to have promoted the view that biology is not an isolated discipline, and that its i -__l; .__. ----%-J . . . VIII natural links with other fields of inquiry deserve explicit recognition and study in their own right. It is a pleasure to record here the many people who have given advice during the preparation of this dictionary, both in formulating entries and in reviewing sections of manuscript. Pupils at Harrow and students at the University of Alberta, Edmonton, have provided valuable criti- cism as consumers. Particular thanks for advice and comments also go to Richard Burden, ‘Michael Etheridge, John Hoddinott, Stephanie Holliday, John Imeson, Bill Richmond, Chris Stringer, Dick Vane- Wright, Dale H. Vitt and two very helpful referees who chose to remain anonymous. Eileen Michie did splendid copy-editing work. It goes without saying that any errors which remain are the sole responsibility of the authors, who would welcome corrections and suggestions for improvement. The dictionary has isolated us from our families, sometimes at rather critical periods, and it is a special pleasure to be able to recognize their patience and forbearance, particularly Katey and Avril, and Margaret, to whom the work is dedicated. M.H. M.T. February 1990 Il‘ ACKNOWLEDGEMENTS FOR FIGURES Some of the original illustrations and/or labelling may have been slightly altered. Alberts, B., et al.: Molecular Biology of the Cell (1st edn), Garland (1983). Figs. 3a, 3b, 6a, 6b, 8, 9, 14, 20,-29,44, 60. Austin, C. R., and Short, R. V.: Reproduction in Mammals, Book 2: Embryonic and Fetal Development (2nd edn), CUP (1982). Figs. 16, 55. Barrington, E. J. W.:s Invertebrate Structure and Function (2nd edn), Nelson (1979). Figs. 17a, 17b, 17~. Chapman, R. F.: The Insects (2nd edn), Hodder & Stoughton (1971). Fig. 49. Charig, A.: A New Look at the Dinosaurs, British Museum (Natural History) (1979). Fig. 63. Cohen, J.: Reproduction, Butterworths (1977). Figs. 62a, 62b. Freeman, W. H., and Bracegirdle, B.: An Advanced Atlas of Histology, Heinemann (1976). Fig. 24. Frobisher, M., et al.: Fundamentals ofMicrobiology (9th edn), Harcourt Brace Jovanovich (1974). Figs. 3c, 30. Goodenough, U.: Genetics (3rd edn), Holt-Saunders (1984). Fig. 38. Grimstone, A. V., Harris, H., and Johnson, R. T.: Prospects in Cell Biology, The Company of Biologists Ltd, Cambridge (1986). Fig. 37. Hartman, P. E., and Suskind, S. R.: Gene Action, Viking Penguin Inc. (1965). Fig. 10. Hopkins, C. R.: Structure and Function of Cells, Harcourt Brace Jovanovich (1978). Figs. 4a, 4b, 5a, 5b, 5c, 5d. Hughes, G. M.: Comparative Physiology of Vertebrate Respiration, Harvard University Press (1963). Figs. 23b, 23~. Katz, B.: Nerve, Muscle and Synapse, McGraw-Hill, Inc. (1966). Fig. 35. Kingley, J. S.: Outlines of Comparative Anatomy of Vertebrates, -The Blakiston Company (McGraw-Hill Book Company) (1928) with permission of McGraw-Hill, Inc. Fig. 23a. Landsborough Thompson, A. (ed.): A New Dictionary of Birds, British Ornithologists’ Union (1964). Figs. 18a, 18b. Lehninger, A. L.: Biochemistry (2nd edn), Worth (1975). Figs. 12a, 12b, 25b, 26,28, 33, 51, 64. Lewis, K. R., and John, B.: The Matter of Mendelian Heredity (2nd edn), Longman (1972). Fig. 42(ij. Mather, K.: Genetical Structure of Populations, Chapman and Hall (1973). Figs. 21a, 21b. May, R. M. (ed.): Theoretical Ecology (2nd edn), Blackwell (1981). Table 5. XX RRoobbeerrttss,, MM.. BB.. VV..:: BBiioollooggyy:: AA FFuunnccttiioonnaall AApppprrooaacchh ((33rrdd eeddnn)),, NNeellssoonn ((11998822)).. FFiiggss.. 5544aa,, 5544bb.. RRoommeerr,, AA.. SS..:: TThhee VVeerrtteebbrraattee BBooddyy ((55tthh eeddnn)),, HHoolltt--SSaauunnddeerrss ((11997777)).. FFiiggss.. 22,, 5522bb,, 5533.. SSllaacckk,, JJ.. MM.. WW..:: FFrroomm EEgggg ttoo EEmmbbrryyoo,, CCUUPP ((11998833)).. FFiigg.. 2222.. SSttaaiinneess,, NN..,, BBrroossttooffff,, JJ..,, aanndd JJaammeess,, KK..:: IInnttrroodduucciinngg IImmmmuunnoollooggyy,, GGoowweerr MMeeddiiccaall ((11998855)).. FFiiggss.. 4411,,4433.. SSzzaallaayy,, FF.. SS..,, aanndd DDeellssoonn,, EE..:: EEvvoolluuttiioonnaarryy HHiissttoorryy ooff tthhee PPrriimmaatteess,, II AAccaaddeemmiicc PPrreessss ((11997799)).. FFiigg.. 3344.. TToorrttoorraa,, GG.. JJ..,, aanndd AAnnaaggnnoossttookkooss,, NN.. PP..:: PPrriinncciipplleess ooffAAnnaattoommyy aanndd PPhhyyssiioollooggyy ((44tthh eeddnn)),, HHaarrppeerr aanndd RRooww ((11998844)).. FFiiggss.. 2255aa,, 2277,,3322,,4400,, 4477,, 5500,, 5522aa,, 5577,,6611aa.. WWaattssoonn,, JJ.. DD..:: MMoolleeccuullaarr BBiioollooggyy ooff tthhee GGeennee ((33rrdd eeddnn)),, BBeennjjaammiinn// .. CCuummmmiinnggss ((11997766)).. FFiigg.. 3399.. A-BAND. See STRIATED MUSCLE. ABAXIAL. (Of a leaf surface) facing away from stem. Compare AD- AXIAL. \ ABDOMEN. (1) Vertebrate body region containing viscera (e.g. in- testine, liver, kidneys) other than heart and lungs; bounded anteriorly in mammals but not other classes by a diaphragm. (2) Posterior arthropod trunk segments, exhibiting,~~~~~~~~ in insects, but not in crustaceans. ABDUCENS NERVE. Sixth vertebrate CRANIAL NERVE. Mixed, but mainly motor, supplying external rectus eye-muscle. ABERRANT CHROMOSOME BEHAVIOUR. Departures from normal mitotic and meiotic chromosome behaviour, often with a recognized genetic basis. Includes (1) achiasmate meiosis, where chiasmata fail to form (e.g. in Drosophila spermatogenesis; see SUPPRESSOR MU - T A TI 0 N); (2) amitosis, where a dumb-bell-like constriction separates into two the apparently ‘interphasellike’, but often highly polyploid, ciliate macronucleus prior to fission of the cell; (3) chromosome extrusion or loss, as with X-chromosomes in egg maturation of some parthenogenetic aphids (see s E x D E T E R M I N A T I 0 N); and . in Drosophila where gynandromorphs may result; but notably in some midges (e.g. Miastor, Heteropeza) where paedogenetic larvae produce embryos whose somatic cells contain far fewer chromo- somes than GERM LINE cells, owing to selective elimination during 1 cleavage (see WEISMANN). In some scale insects, males and females develop from fertilized eggs, but males are haploid because the entire paternal chromosome set is discarded at cleavage (see HE T - EROCHROMATIN, PARASEXUALITY, GYNOGENESIS); (4) meiotic drive, where a mutation causes the chromosome on which it occurs to be represented disproportionately often in gametes produced by meiosis, as with the segregation distorter (SD) locus of Drosophila; mutants homozygous for the SD allele are effectively sterile; (5) premeio tic chromosome doubling (see A u T 0 M I x I s); (6) E N D 0 - MITOSIS, where chromosomes replicate and separate but the nucleus and cell do not divide; (7) POL Y TEN Y, where DNA replication occurs but the strands remain together to form thick, giant chromosomes. ABIOTIC. Environmental features, such as climatic and ED A PH I c factors, that do not derive directly from the presence of other organisms. See BIOTIC. -: 1 - ABOMASSUM 2 LL ABOMASSUM. The ‘true’ stomach of RUMINANTS. +L s __ ABSCISIC ACID (ABSCISIN, DORMIN). Inhibitory plant GROWTH SUB- / - STANCE (a sesquiterpene). Present in a variety of plant organs - ’ , leaves, buds, fruits, seeds and tubers. Promotes senescence and ab- 1 scission of leaves; induces dormancy in buds and seeds. Antagonizes I--- influences of growth-promoting substances. Believed to act by inhibit- ing nucleic acid and protein synthesis. ABSCISSION LAYER. Layer at base of leaf stalk in woody dicotyledons and gymnophytes, in which the parenchyma cells become separated \ *from one another through dissolution of the middle lamella before leaf-fall. ABSORPTION SPECKS Graph of light absorption versus wavelength of incident light. Shows how much light (measured as quanta) is absorbed by a pigment (e.g. plant pigments) at each wavelength. CO~paIXACTIONSPECTRUM.‘ ABYSSAL. Inhabiting deep water, roughly below 1000 metres. ACANTHODII. Class of primitive, usually minnow-sized, fossil fish . abundant in early Devonian freshwater deposits. Earliest known gnathostomes. Bony skeletal tissue. Fins supported by very stout spine; several accessory pairs of fins common. Row of spines between pectoral and pelvic fms. Heterocercal tail. Relationships with os- teichthyan fishes uncertain, but probably not directly ancestral. See PLAeODERMI.. ACANTHOPTERYGII. Spmy-rayed fish. Largest superorder of (teleost) fishes. Spiny rays in their fins consist of solid pieces of bone (and not numerous’small bony pieces); are unbranched and pointed at their tips. Radial bones of each ray are sutured or fused, preventing relative lateral movement. Often have short, deep bodies,.and relatively large ; fins, making these fish very manoeuvrable. See TELEOSTEI. I ACARI (OCARINA). Order of ARACHNIDA including mites and ticks. -External segmentation much reduced or absent. Larvae usually with ‘- three pairs of legs, nymphs land adults with four pairs. Of considerable I economic and social importance as many are ectoparasites and vec- tors of pathogens. :.- ACCESSORY BUD. A bud generally situated above or on either side of main axillary bud. ) I ACCESSORYCHROMOSOME. S~~SUPERNUMERARY CHROMOSOME. ACCESSORY NERVE. Eleventh cranial nerve of tetrapod vertebrates, unusual in originating from both brain stem and spinal cord. A mixed nerve, whose major motor output Js to muscles of throat, neck and viscera. 3 ACHENE ACCESSORY PIGMENT. Pigment that captures light energy and transfers it to chlorophyll a, e.g. chlorophyll b, carotenoids, phycobiliproteins. ACCOMMODATION. Changing the focus of the eye. In man and a few other mammals occurs by changing the curvature of the lens; at rest lens is focused for distant objects and is focused for near objects by becoming more convex with contraction of the ciliary muscles in the CILIARY BODY.SeeEYE,OCULOMOTOR NERVE. ACELLULAR. Term sometimes applied to organisms or their parts in which no nucleus has sole charge of a specialized part of the cyto- plasm, as in unicellular organisms. Applicable to coenocytic or- ganisms (e.g. many fungi), and to tissues forming a SYNCYTIUM. Sometimes preferred to ‘unicellular’. See Mu L T I C E L L u LA R 1 T Y. ACENTRIC. (Of chromosomes) chromatids or their fragments lacking ally CENTROMERES. , ACETABULUM. Cup-like hollow on each side of hip girdle into which head of femur (thigh bone) fits, forming hip joint in tetrapod vertebrates. See PELVIC GIRDLE. ACETIFICATION. See FERMENTATION. ACETYLCHOLINE (Ach). NEUROTRANSMITTER of many interneural, neuromuscular and other chdinergic effector synapses. Relays elec- trical signal in chemical form, with transduction back to electrical c$ signal at the postsynaptic membrane. Initiates depolarization of postsynaptic membranes to which it binds; but hyperpolarizes ve- w-gw in sY~!~?%%&%% inside-253riire-leased there in quanta1 fashion in response to calcium ion uptake on arrival of an ACTION POTENTIAL. It diffuses across the synaptic cleft and binds to receptor sites on the postsynaptic membrane, whereupon these ion _ __ channels open and allow appropriately sized positive ions to, enter cell, initiating membrane depolarization. Hydrolysis to choline and the postsynaptic membrane ropriately brief (see SUM MA- TION). Vertebrate ACh postsynaptic receptors are distinguished as nicotinic or muscarinic on the results of alkaloid administration. -?%6IEZ receptors-(@nglia, neuromuscular junctions and possibly \ some brain and spinal cord regions) are blocked by curare, muscarinic (peripheral autonomic interneural synapses) by atropine. ACh is found in some protozoans.Compare ADRENERGIC. j ACETYLCHOLINESTERASE. See CHOLINESTERASE. ACETYL COENZYMEA. See COENZYME A. ACHENE. Simple, dry, one-seeded fruit formed from a single carpel, 8 without any special method of opening to liberate seed; seed coat is