Chap. XIII. 
CLASSIFICATION. 
411 
CHAPTEE XIIL 
Mutual Affinities of Organic Beings : Morphology : 
Embryology : Eudimentary Organs. 
Classification, groups subordinate to groups — Natural system — 
Eules 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 
separates 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 —- 
Eudimentary organs ; their origin explained — Summary. 
From the first dawn of life, all organic beings are found 
to resemble each other in descending degrees, so that 
they can be classed in groups under groups. This classi¬ 
fication is evidently not arbitrary like the grouping of 
the stars in constellations. The existence of groups 
would have been of simple signification, if one group had 
been exclusively fitted to inhabit the land, and another 
the water; one to feed on flesh, another on vegetable 
matter, and so on; but the case is widely different in 
nature; for it is notorious how commonly members of 
even the same sub-group have different habits. In 
our second and fourth chapters, on Variation and on 
Natural Selection, I have attempted to show that it is 
the widely ranging, the much diffused and common, that 
is the dominant species belonging to the larger genera, 
which vary most. The varieties, or incipient species, 
thus produced ultimately become converted, as I believe, 
into new and distinct species; and these, on the principle 
of inheritance, tend to produce other new and dominant 
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