The Making of Species 
CHAPTER III 
PAGE 
VARIATION. , . . ‘ z 52 
The assumption of Darwin and Wallace that variations are haphazard 
in origin and indefinite in direction—If these assumptions be 
not correct Natural Selection ceases to be the fundamental factor 
in evolution—Darwin’s views regarding variation underwent 
modification—He eventually recognised the distinction between 
definite and indefinite variations, and between continuous and 
discontinuous variations—Darwin attached but little importance 
to either definite or discontinuous variations—Darwin’s views on 
the causes of variations—Criticism of Darwin’s views—Variations 
appear to occur along certain definite lines—There seems to be 
a limit to the extent to which fluctuating variations can be 
accumulated—De Vries’ experiments—Bateson on ‘‘discon- 
tinuous variation” — Views held by De Vries— Distinction 
between continuous and discontinuous variations—The work of 
De Vries—Advantages enjoyed by the botanist in experimenting 
on the making of species—Difficulties encountered by the 
animal breeder—Mutations among animals—The distinction 
between germinal and somatic variations—The latter, though 
not transmitted to offspring, are often of considerable value to 
their possessor in the struggle for existence. 
CHAPTER IV 
Hypripism 2 ‘ < a zs IIr 
The alleged sterility of hybrids a stumbling-block to evolutionists— 
Huxley’s views—Wallace on the sterility of hybrids—Darwin on 
the same—Wallace’s theory that the infertility of hybrids has 
been caused by Natural Selection so as to prevent the evils of 
intercrossing—Crosses between distinct species not necessarily 
infertile—Fertile crosses between species of plants—Sterile plant 
hybrids—Fertile mammalian hybrids—Fertile bird hybrids— 
Fertile hybrids among amphibia—Limits of hybridisation— 
Multiple hybrids—Characters of hybrids—Hybridism does not 
appear to have exercised much effect on the origin of new 
species. 
CHAPTER V 
INHERITANCE . ‘ : p : - 133 
Phenomena which a complete theory of inheritance must explain— 
In the present state of our knowledge it is not possible to 
formulate a complete theory of inheritance—Different kinds of 
inheritance—Mendel's experiments and theory—The value and 
xiv 
