Chap. VI. 
DIFFICULTIES ON THEOKY, 
171 
CHAPTEE VI. 
Difficulties on Theory. 
Difficulties on tTie tlieory 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. 
Long before having arrived at this part of my work, a 
crowd of difficulties will have occurred to the reader. 
Some of them are so grave that to this day I can never 
reflect on them without being staggered; but, to the best 
of my judgment, the greater number are only apparent, 
and those that are real are not, I think, fatal to my 
theory. 
These difficulties and objections may be classed under 
the following heads:—Firstly, why, if species have 
descended from other species by insensibly fine grada¬ 
tions, do we not everywhere see innumerable transitional 
forms ? Why is not all nature in confusion instead of 
the species being, as we see them, well defined ? 
Secondly, is it possible that an animal having, for 
instance, the structure and habits of a bat, could have 
been ^formed by the modification of some animal with 
wholly different habits ? Can we believe that natural 
selection could produce, on the one hand, organs of 
trifling importance, such as the tail of a giraffe, which 
serves as a fly-flapper, and, on the other hand, organs of 
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