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 --
Modes 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.


CHAPTER VII.

MISCELLANEOUS OBJECTIONS TO THE THEORY OF NATURAL SELECTION.

Longevity -- Modifications not necessarily simultaneous -- Modifications
apparently of no direct service -- Progressive development -- Characters of
small functional importance, the most constant -- Supposed incompetence of
natural selection to account for the incipient stages of useful structures
-- Causes which interfere with the acquisition through natural selection of
useful structures -- Gradations of structure with changed functions --
Widely different organs in members of the same class, developed from one
and the same source -- Reasons for disbelieving in great and abrupt
modifications.


CHAPTER VIII.

INSTINCT.

Instincts comparable with habits, but different in their origin --
Instincts graduated -- Aphides and ants -- Instincts variable -- Domestic