CHAPTER V.

LAWS OF VARIATION.

Effects of external conditions--Use and disuse, combined with natural selection; organs of flight and of vision--Acclimatisation--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

131-170

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