CHAPTER VIII.
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, molothrus,
ostrich, and parasitic bees -- Slave-making ants -- Hive-bee, its cell-
making instinct -- Changes of instinct and structure not necessarily
simultaneous -- Difficulties on the theory of the Natural Selection of
instincts -- Neuter or sterile insects -- Summary.
CHAPTER IX.
HYBRIDISM.
Distinction between the sterility of first crosses and of hybrids --
Sterility various in degree, not universal, affected by close
interbreeding, removed by domestication -- Laws governing the sterility of
hybrids -- Sterility not a special endowment, but incidental on other
differences, not accumulated by natural selection -- Causes of the
sterility of first crosses and of hybrids -- Parallelism between the
effects of changed conditions of life and of crossing -- Dimorphism and
Trimorphism -- Fertility of varieties when crossed and of their mongrel
offspring not universal -- Hybrids and mongrels compared independently of
their fertility -- Summary.
CHAPTER X.
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 lapse
of time, as inferred from the rate of denudation and of deposition -- On
the lapse of time as estimated in years -- On the poorness of our
palaeontological collections -- On the intermittence of geological
formations -- On the denudation of granitic areas -- 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 -- Antiquity of the habitable earth.
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