[PDF]A Dictionary of biology

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DICTIONARY
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BIOLOGY


M. Abercrombie
C. J. Hickman
M. L. Johnson


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Some Other E.L.B.S. Titles


Clare, F.

The Stuff of Life

Flood, W. E. and West, M.

An Elementary Scientific and Technical Longmans
Dictionary

Hornby, A. S. and Parnwell, E. G.


Phoenix House


An English Reader’s Dictionary Oxford
Isaacs, A.

Introducing Science Penguin
Kelly, R. A.


The Use of English for Technical Students Harrab
Livingstone’s Pocket Medical Dictionary Livingstone
(Formerly known as “Lois Oakes
Pocket Medical Dictionary’)
Uvarov, E. B., Chapman, D. R. and Isaacs, A.


A Dictionary of Science Penguin


4s. od.


4s. 6d.


gs. 6d.
2s. od,


4s. 6d.
3s. 6d,


2s. od.


A DICTIONARY OF
Biology


M. ABERCROMBIE, C. J. HICKMAN,
AND M. L. JOHNSON


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SEENGHING: BOOKS


Compiled specially for Penguin Books and first published 1951
Reprinted 1951
Enlarged and revised edition 1954
Reprinted 1955
Revised edition 1957
Reprinted 1958, 1959, 1960

Revised edition 1961
Reprinted 1961, 1962, 1963, 1964, 1965
Revised edition 1966
Reprinted 1968
E.L.B.S, edition first published 1964
Reprinted 1968


Copyright © M. Abercrombie, C. J. Hickmann,
and M. L. Johnson, 1951


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Made and printed in Great Britain
by Hunt Barnard & Co. Ltd, Aylesbury
Set in Monotype Baskerville


AUTHORS’ NOTE


THERE are well over a million organisms, each with a
name, and tens of thousands of other biological terms.
In selecting a mere two thousand for definition we must
often have chosen badly. Similarly, we have been forced
to limit severely the amount of information we present
under each heading, and may well have misplaced the
emphasis on many occasions, We should be glad to have
comments about these points, and about inaccuracies of
fact, from users of the dictionary.

Our grateful thanks go to our friends and colleagues `
whose criticisms and suggestions have greatly assisted
us in the preparation and revision of the dictionary.

M. A.
C. J. H.
M. L. J.


USING THE DICTIONARY


Many unfamiliar terms, especially the rarer ones, are defined
with the help of other technical terms, perhaps equally un-
familiar. This annoying trick of dictionary-makers could only
be avoided by giving a complete account of a large part of
biology under each heading, which is impracticable. There is
nothing for it but to follow up the terms until you come to an
entirely intelligible definition. Every biological technical term
used in a definition is, we believe, itself defined elsewhere in
the dictionary; though some semi-technical terms, which can
be found in any English Dictionary (such as the Pocket
Oxford), are omitted.

We put the letters (q.v.) after a term which is defined else-
where only when its definition adds important information to
the subject under discussion. It is not put after every term
defined elsewhere. The letters Cf. are intended to point out a
contrasting term,

(Bot.) or (Zool.) before a definition means that what follows
applies only to plants or to animals respectively. It is not used
where the limitation is obvious,

(Adj.) means that the term defined is an adjective, when
this is not clear from the definition.

If a word is not defined in the dictionary, try Uvarov’s
Dictionary of Science (Penguin Reference Book R1); and consult
it for supplementary information on any chemical term.


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A


ABAXIAL (Dorsal). (Of a leaf surface), facing away from the stem.
Cf. Adaxial.

ABDOMEN. In vertebrates: region of the body containing the viscera
other than heart and lungs (i.e. intestine, liver, kidneys, etc.);
in mammals, but not in other vertebrates, bounded anteriorly by
diaphragm. In arthropods: posterior group of segments similar to
each other.

ABDUCENS NERVE. Sixth cranial nerve of vertebrates. Almost
entirely motor, supplying external rectus eye-muscle. See Eye-
muscles. A ventral root.

ABIOGENESIS. Spontaneous generation (q.v.).

ABsaIsin. Hormone-like substance having accelerating effect on
leaf abscission. May be competitive inhibitor of auxin action.
Present in senescent leaves. Also obtained from fruits of several
plants and involved in abscission of later formed flowers or of young
fruit. A substance named dormin, shown to be identical with abscisin,
occurs in leaves of some woody plants in autumn (and in leaves of
plants exposed to short-day conditions) and induces bud dormancy
in these plants,

ABSCISSION LAYER, Layer at base of leaf-stalk in woody dicotyle-
dons and gymnosperms, in which the parenchyma cells become
separated from one another through dissolution of the middle
lamella before leaf-fall.

ABYSSAL. Inhabiting deep water (roughly below 1,000 metres).

ACANTHODII. Group of fossil fish (mainly Devonian, 350 to 400
million years ago, but lasted through 150 million years to Perm-
ian). An order of Placodermi. Notable because many of them had
not only pectoral and pelvic fins, but a row of other paired fins
between them, each bearing a prominent spine along its anterior
margin.

ACARINA (ACARIDA). Order of Arachnida including mites and
ticks; some are important parasites, e.g. Sarcoples causing scabies,
cattle tick carrying redwater fever.

ACCESSORY NERVE. Eleventh cranial nerve of tetrapod vertebrates. |
Really a branch of the vagus, clearly separate only in mammals.
ACCOMMODATION. Changing the focus of the eye. In man and a
few other mammals occurs by changing curvature of lens; at rest,
lens is focused for distant objects; it is focused for near objects
by becoming more convex with the contraction of the ciliary
muscles in ciliary body (q.v.) (see Fig. 3, p. 97)- Few mammals can
accommodate. Most birds and reptiles accommodate by changing
curvature of the lens; in fish and amphibians, lens is moved back-
wards and forwards in relation to retina (as in focusing a camera).
ACELLULAR. (Of an organism), not divided into separate cells,


8 ACETABULUM


Many organisms consisting of one cell are quite complex in structure
and in function and, in contrast to the term unicellular, ‘acellular’
emphasizes the biological equivalence of such organisms to the
whole of a multicellular organism rather than to one of its cells.

ACETABULUM. Cup-like hollow on each side of hip girdle into which
head of femur (thigh bone) fits, forming hip joint, in tetrapod
vertebrates,

ACETYLCHOLINE (ach). Substance secreted at the ends of many
nerve fibres (cholinergic fibres) when nerve impulses arrive there.
Where such a nerve fibre ends at a synapse, e.g. in sympathetic and
parasympathetic ganglia, ACh is the agent which stimulates the
contiguous nerve cell and hence in effect ‘passes the impulse on’;
and similarly where the fibre connects with an effector, e.g. at the
nerve-muscle junction. After secretion ACh is very rapidly destroyed
by the enzyme cholinesterase, being broken down into acetate and
choline, It is the acetyl ester of choline (q.v.).

ACHENE. Dry, one-seeded fruit formed from a single carpel, with no
special method of opening to liberate the seed; may be smooth-
walled, e.g. buttercup; feathery, e.g. traveller’s joy; spiny, e.g.
corn buttercup; or winged (samara), e.g. sycamore.

ACHLAMYDEOUS. (Of flowers), lacking petals and sepals, e.g. willow.

ACID DYES. Dyes consisting of an acidic organic grouping of atoms
(anion) which is the actively staining part, combined with a metal.
Stain particularly cytoplasm and collagen. Cf. Basic dyes.

ACOELOMATE, Having no coelom (e.g. the phyla Coelenterata,
Platyhelminthes, Nemertea, Nematoda).

acoustic, Concerned with hearing. A. nerve, Auditory nerve (q.v.).

ACQUIRED CHARACTERISTICS, INHERITANCE OF, Transmission

to offspring of variations, which appeared in the parents as re-
sponses to environmental influences. E.g. exposure to sunlight
causes darkening of the skin of white human beings, compared to
others less exposed: an acquired characteristic. If this acquired
characteristic were inherited, offspring of the darker parents would
then tend, even if only very slightly, to be darker than offspring of
the lighter parents, when both groups of offspring are reared in
equal sunlight. The view that such inheritance occurs is commonly
known as Lamarckism (q.v.) or Neo-Lamarckism. It is not widely
thought that such inheritance is of importance in organisms repro-
ducing sexually. When an acquired variation occurs, the gametes
are not usually affected in such a way as to reproduce these varia-
tions in the offspring. It has however been shown that natural
selection (q.v.) may change successive generations of a population
so that a characteristic at first acquired only in response to the
environment may come to develop independently of the environ-
mental stimulus (genetic assimilation). Organisms reproducing
asexually may, of course, hand on to their offspring part of the body
complete with its acquired characteristics.


ACTINOZOA (ANTHOZOA) 9


AGRANIA (CEPHALOCHORDATA). Sub-phylum of Chordata con-
taining only species of amphioxus, all marine. Unlike Vertebrata
they have no brain, skull, or cartilaginous or bony skeleton; but
they have typical chordate dorsal tubular nerve-cord with double
nerve roots, notochord, gill-slits, muscle blocks (myotomes) ; and
they have an unexpected feature, found in no other chordate
though in many invertebrates — nephridia as excretory organs.
They may be closely related to early ancestors of fish and other
vertebrate groups. A very early fossil probably belonging to the
group has been discovered (Zaymoytius from the Silurian).

ACRASIALES. Cellular or communal slime moulds. Group (Order)
characterized by aggregation, but not coalescence, of amoebae to
form a pseudoplasmodium. Form spores in minute inconspicuous
fructifications (sporocarps). Affinity uncertain. See Myxomyco-
phyta.

ACROPETAL. (Bot.). Development of organs in succession towards
apex, the oldest at base, youngest at tip, e.g. leaves on a shoot. Also
used in reference to direction of transport of substances within a
plant, i.e. towards the apex. Cf. Basipetal.

ACROSOME. Part of head of animal sperm, usually forming a
cap over the nucleus. It is concerned in penetration into the egg
during fertilization.

ACTH (CORTICOTROPIN). Adreno-cortico-tropic hormone, a
polypeptide secreted by anterior lobe of pituitary, controlling
secretory activity of adrenal cortex, particularly the secretion of
glucocorticoids. Its own rate of secretion is controlled by a poly-
peptide hormone liberated from the hypothalamus.

AcTINOMoRPHICG. (Of flowers), regular; capable of bisection vertic-
ally in two or more planes into similar halves, e.g. buttercup. Also
known as radially symmetrical, a term used to describe animals hav-
ing asimilar organization, e.g. jelly-fish. Cf. Zygomorphic.

ACTINOMYCETE. Member of genus Actinomyces, group of gram-
positive bacteria with cells arranged in hypha-like filaments,
parasitic in mammals.

ACTINOPTERYGII. A class of fish (or sometimes regarded as a sub-
class of the class Osteichthyes); includes all common fish except
sharks and skates. Characterized by bony skeleton; absence of a
central skeletal axis in paired fins, their skeletal support being like
the ribs of a fan; no opening of nostrils into mouth. Ganoid scales
(q.v.) in primitive species. Gf. Chondrichthyes and Choanichthyes, the
other two classes of living fish. Appear first in Devonian (350 to 400
million years ago) ; originally fresh-water, but later colonized the
sea.

ACTINOZOA (ANTHOZOA). Sea-anemones, corals, sea-pens, etc.
Class of Coelenterata (of subphylum Cnidaria). No medusa stage;
polyp more complexly organized than that of other Coelenterata;
possessing an intucking of ectoderm into coclenteron (stomo-


10 ACTION POTENTIAL


daeum); and vertical partitions in coelenteron (mesenteries). See
Alcyonaria. Cf. Hydrozoa, Scyphozoa.

ACTION POTENTIAL. Of a nerve impulse; a localized change of
electrical potential between the inside and outside of a nerve fibre,
which marks the position of an impulse as it travels along the fibre. j
In the absence of an impulse the inside is electrically negative to
the outside (the resting potential); and during the passage of an
impulse past any point on the fibre it changes momentarily to
positive. This wave of potential change is the most easily detectable
and measurable aspect of an impulse. A similar action potential’
occurs in a muscle fibre when it is stimulated.

ACTION SPECTRUM. Wavelengths (A) that are active in promoting
or inhibiting a particular reaction, e.g. action spectra for photo-
synthesis show maximum absorption and activity in blue and red
parts of visible spectrum.

ACTIVATED SLUDGE. Material consisting largely of Bacteria and
Protozoa, used in, and produced by, one method of sewage dis-
posal. Sewage is mixed with some activated sludge and agitated
with air; organisms of the sludge multiply and purify the sewage, }
and when it is allowed to settle they separate out as a greatly
increased amount of activated sludge. Part of this is added to new
sewage and part disposed of.

ACTIVE CENTRE (SITE). The part of an enzyme molecule that
combines with the substrate. A relatively small number of the
atoms of the enzyme molecule are involved.

ACTIVE TRANSPORT. Transfer of substance from region of low to
region of high concentration, accomplished by means of expendi- >
ture of energy from metabolism. Probably all cells can do this.

ACTOMYOSIN. A complex of two proteins, actin and myosin, forming
a major constituent of muscle. Shortening of actomyosin fibrils
produces contraction of muscles. Myosin is very closely associated 7
with an enzyme whose activity liberates energy for this contraction i
from ATP (q.v.).

ACUSTICO“LATERALIS SYSTEM. Lateral line system (q.v.). b:

ADAPTATION. (1) Evolutionary. Any characteristic of living organ-
isms which, in the environment they inhabit, improves their chan- i
ces of survival and ultimately of leaving descendants, in comparison 1

4


with the chances of similar organisms without the characteristic; ¥
natural selection therefore tends to establish adaptations in a popù-
lation. An adaptation to a particular feature of the environment 7
means a characteristic which is an adaptation because it reduces wil,
destruction by that particular feature. An adaptation to a particu- {
lar activity of an organism (e.g. to flying) means simply a character-
istic which makes possible or improves performance of that activity _
without necessarily being measured in terms of survival, though ©
usually that is implied. (2) Physiological. Change in an organism as
a result of exposure to certain environmental conditions which
I Miaa


ADRENAL (SUPRARENAL) GLAND Ir


makes it react more effectively to these conditions. (3) Sensory.
Change in excitability of a sense-organ as a result of continuous
stimulation such that a more intense stimulus becomes necessary to
produce the same response. E.g. contact of an object with the skin at
once excites the touch receptors; but if contact is simply maintained
the touch receptors quickly cease to respond, though they will
respond again to a more intense stimulus. Different receptors differ
much in the extent of their adaptation.

ADAPTIVE (INDUCIBLE) ENZYME. Enzyme formed by an organism
in appreciable amounts only in response to the presence of its sub-
strate or a similar substance. Bacteria especially are known to
adjust their enzyme make-up in this way. Cf. Constitutive Enzyme.

ADAPTIVE RADIATION. Evolution, from a primitive type of organ-
ism, of several divergent forms adapted to distinct modes of life.
E.g. at beginning of Tertiary the basal stock of placental mammals
radiated into many forms adapted to running, flying, swimming,
burrowing, etc.

ADAXIAL. (Ofa leaf surface), facing the stem. Cf. Abaxial.

ADENOHYPOPHYSIS. See Pituitary Body.

ADENOSINE TRIPHOSPHATE. ATP (q.v.).

ADIPOSE TISSUE, Fatty tissue. Connective tissue, the cells of which
contain large globules of fat.

ADP (ADENOSINE DIPHOSPHATE), Co-enzyme, associated in energy
transfer in living organisms with ATP (q.v.).

ADRENAL (SUPRARENAL) GLAND. An organ of hormone secretion
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