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On the generality of intercrosses between individuals of the same species—Cir cumstances favourable and unfavourable to Natural Selection, namely, intercrossing, isolation, number of individuals—Slow action-- Extinction caused by Natural Selection—Divergence of Character, 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, ....... TT
LAWS Of Y A R"I A T I O W .
Effects of external conditions—Use and disuse, combined with natural selection organs of flight and of vision—Acelimatisation—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, . . . . . 120
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 faclt saltum—Organs of small importance—Organs-irot in all cases absolutely perfect—The law of Unity of Type and of tho Conditions of Existence embraced by the theory of Natural Selection, ...... 1M
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 ante—Hive-bee, its cell-making instinct—Difficulties on tho theory of the Natural Selection of instincts—Neuter or sterile insects—Summary, . . . . .181
Distinction betwecn,tho sterility of first crosses and of hybrids—Sterility various in degree, not universal, affected by close interbreeding, removed by domestication— Laws governing tho 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 tho effects of changed conditions of life and cross> lug—Fertility of varieties when crossed and of their mongrel offspring not uni versal—Hybrids and mongrels compared independently of their fertility—Summary ,217
OK THE IMPERFECTION 07 THE GEOLOGICAL RECORD.
On tho absence of intermediate varieties at the present day—On the nature of extinct Intermediate varieties j on their number—On the vast lapse of time, as inferred from the rate of deposition and of denudation—On the poorness of our palceontological collections—On the lntermlttenco 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, . 2U
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 appearance and disappearance as do single species—On Extinction—On simultaneous changes in the forms of life throughout tho 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 aud present chapters, .... 273
Present distribution cannot be accounted for by differences in physical conditions—Importance of barriers—Affinity of the productions of tho 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 802
aEOGRApniCAL Distrihl-tion— Continued.
Distribution of fresh-water [productions—On tho inhabitants of oceanic islands—Absence of Batrachlans and of terrestrial mammals—On tho relation of tho inhabitants of islands to those of the nearest mainland—On colonisation from the nearest source with subsequent modification—Summary of tho last and present chapters, Ki4
BCTCAL AFFINITIES OF ORGANIC BEINGS I M0RpHOLO0T I EMBRTOLOGT: RUDIKEKTAET ORGANS.
Classification, groups subordinate to groups—Natural system—Rules and difficulties in ciassification, explained on the theory of descent with modification—Classi' float ion of varieties—Descent always used in classification—Analogical or adaptive characters—Affinities, general, complex and radiating—Extinction separates and defines groups—MoRpbOLOor, between members of tho same class, between parts of the same individual —Embrtoloor, laws of, explained by variations not supervening at an early age, and being inherited at a corresponding age —Rudimintart OMUI; their origin explained—Summary, . . . . .351
RKCAPITtJLATION AND CONCLUSION.
Recapitulation of the difficulties on tho theory of Natural Selection—Recapitulation of the general and special circumstances in its favour—Causes of tho 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, .......... 898
ON THE ORIGIN OF SPECIES.
When on board H. M. S. 1 Beagle' as naturalist, I was
My work is now nearly finished; but as it will take
Society. Sir C. Lyell and Dr. Hooker, who both knew
This Abstract, which I now publish, must necessarily
I much regret that want of space prevents my having
In considering the Origin of Species, it is quite con-
is published in the third volume