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PENGUIN BOOKS
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PENGUIN BOOKS i
Published by the Penguin Group
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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
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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
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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.
-:
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-
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
