CHAPTER III.

STRUGGLE FOR EXISTENCE.

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-

Bears on natural selection-The term used in a wide sense-Geo-
metrical powers of increase Rapid increase of naturalised
animals and plants-Nature of the checks to increase-Compe-
tition universal - Effects of climate Protection from the
number of individuals-Complex relations of all animals and
plants throughout nature-Struggle for life most severe between
individuals and varieties of the same species; often severe be-
tween species of the same genus-The relation of organism to
organism the most important of all relations

Natural Selection -

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CHAPTER IV.

NATURAL SELECTION.

Page 60-79

its power compared with man's selection-its
power on characters of trifling importance—its power at all ages
and on both sexes Sexual Selection - On the generality of inter-
crosses between individuals of the same species Circumstances
favourable and unfavourable to Natural Selection, namely,
intercrossing, isolation, number of individuals - Slow action
Extinction caused by Natural Selection Divergence of Cha-
racter, related to the diversity of inhabitants of any small area,
and to naturalisation - Action of Natural Selection, through
Divergence of Character and Extinction, on the descendants
from a common parent- Explains the Grouping of all organic
beings

80-130

CHAPTER V.

LAWS OF VARIATION.

Effects of external conditions - Use and disuse, combined with
natural selection; organs of flight and of vision — Acclimatisa-
tion - Correlation of growth Compensation and economy of
growth-False correlations - Multiple, rudimentary, and lowly
organised structures variable-Parts developed in an unusual
manner are highly variable: specific characters more variable
than generic secondary sexual characters variable - Species of
the same genus vary in an analogous manner - Reversions to
long-lost characters-Summary

131-170

CHAPTER VI.

DIFFICULTIES ON THEORY.

Difficulties on the theory of descent with modification-Transitions-
Absence or rarity of transitional varieties-Transitions in habits
of life-Diversified habits in the same species-Species with
habits widely different from those of their allies-Organs of
extreme perfection-Means of transition-Cases of difficulty-
Natura non facit saltum-Organs of small importance-Organs
not in all cases absolutely perfect-The law of Unity of Type
and of the Conditions of Existence embraced by the theory of
Natural Selection
Page 171-206

CHAPTER VII.

INSTINCT.

Instincts comparable with habits, but different in their origin
Instincts graduated - Aphides and ants - Instincts variable-
Domestic instincts, their origin — Natural instincts of the cuckoo,
ostrich, and parasitic bees - Slave-making ants — Hive-bee, its
cell-making instinct — Difficulties on the theory of the Natural
Selection of instincts-Neuter or sterile insects - Summary

-

207-244

CHAPTER VIII.

HYBRIDISM.

Distinction between the sterility of first crosses and of hybrids
Sterility various in degree, not universal, affected by close inter-
breeding, removed by domestication-Laws governing the sterility
of hybrids - Sterility not a special endowment, but incidental
on other differences Causes of the sterility of first crosses and
of hybrids - Parallelism between the effects of changed con-
ditions of life and crossing - Fertility of varieties when crossed
and of their mongrel offspring not universal Hybrids and
mongrels compared independently of their fertility-Summary

245-278

CHAPTER IX.

ON THE IMPERFECTION OF THE GEOLOGICAL RECORD.

On the absence of intermediate varieties at the present day-On
the nature of extinct intermediate varieties; on their number
On the vast lapse of time, as inferred from the rate of deposi-
tion and of denudation On the poorness of our palæontological
collections On the intermittence of geological formations
On the absence of intermediate varieties in any one formation
-On the sudden appearance of groups of species - On their
sudden appearance in the lowest known fossiliferous strata

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Page 279-311

CHAPTER X.

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ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS.,
On the slow and successive appearance of new species-On their
different rates of change-Species once lost do not reappear
Groups of species follow the same general rules in their appear-
ance and disappearance as do single species — On Extinction
On simultaneous changes in the forms of life throughout the
world - On the affinities of extinct species to each other and to
living species-On the state of development of ancient forms
On the succession of the same types within the same areas
Summary of preceding and present chapters
312-345

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CHAPTER XI.

GEOGRAPHICAL DISTRIBUTION.

Present distribution cannot be accounted for by differences in phy-
sical conditions - Importance of barriers- Affinity of the pro-
ductions of the same continent - Centres of creation - Means
of dispersal, by changes of climate and of the level of the land,
and by occasional means ·Dispersal during the Glacial period
co-extensive with the world ..

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346-382

CHAPTER XII.

GEOGRAPHICAL DISTRIBUTION-continued.

Distribution of fresh-water productions - On the inhabitants of
oceanic islands - Absence of Batrachians and of terrestrial Mam-
mals-On the relation of the inhabitants of islands to those of
the nearest mainland - On colonisation from the nearest source
with subsequent modification-Summary of the last and pre-
sent chapters
Page 383-410

CHAPTER XIII.

MUTUAL AFFINITIES OF ORGANIC BEINGS: MORPHOLOGY:
EMBRYOLOGY: RUDIMENTARY ORGANS.

CLASSIFICATION, groups subordinate to groups-Natural system -
Rules and difficulties in classification, explained on the theory of
descent with modification Classification of varieties - Descent
always used in classification — Analogical or adaptive characters
— Affinities, general, complex and radiating-Extinction se-
parates and defines groups MORPHOLOGY, between members
of the same class, between parts of the same individual—
EMBRYOLOGY, laws of, explained by variations not supervening
at an early age, and being inherited at a corresponding age
– RUDIMENTARY ORGANS; their origin explained - Summary
411-458

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CHAPTER XIV.

RECAPITULATION AND CONCLUSION.

Recapitulation of the difficulties on the theory of Natural Selection
Recapitulation of the general and special circumstances in its
favour Causes of the general belief in the immutability of
species- How far the theory of natural selection may be
extended-Effects of its adoption on the study of Natural
history Concluding remarks

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459-490

491

b

INSTRUCTION TO BINDER.

The Diagram to front page 117, and to face the latter part of the

Volume.