Contents ix 
CHAPTER XII 
PAGE 
INBREEDING . 6 ‘ . . . 7 . . . . - 186 
Experiments with Mice and Rats : : F - : - 188 
Experiments with the Pomace Fly , , . : - - 190 
Behavior of Germ-cells in Inbreeding . ‘ : . . ‘ + 195 
CHAPTER XIII 
INFLUENCE OF SELECTION . i F ‘i : f : . - 198 
Fluctuating or Individual Differences . ‘ ‘ i é » 199 
Selection of Fluctuating Differences . : z : - . + 202 
Elimination within the Species. ‘ . . : - é - 204 
Variation and Parthenogenesis. 206 
The Results of Selection and Hy bidibation af Wild Wlenentary Spadies 207 
Selection under Domestication of Mutations, Saltations, Sports, and 
Discontinuous Varieties in General . ‘ : . . 208 
CHAPTER XIV 
THE THEORY OF EVOLUTION . : - . : ‘ . . + 213 
The Analogy with Artificial Selection . : J ; é 3 - 214 
The Influence of the Environment . : zs : . 215 
De Vries’s Results with CEnothera : : : : , ‘ . 217 
Variation and Mutation in Helix . r : : : F 221 
Evolution by Means of Definite Variation . : a : . . 224 
Adaptation . ‘ . 229 
The Selection Theory and the Theory ot he Sucvivel of Mutations . 232 
EXPERIMENTAL STUDY OF GROWTH 
CHAPTER XV 
INTRODUCTORY . . F : : : : . . - - 239 
Normal Growth . é F : ‘ . > . : is 239 
Senescence . A : : : é : j . 246 
Length of Life in Different Srecits : 2 H | 248 
Absorption of Parts by Larve . . : . : : ‘ + 251 
CHAPTER XVI 
EXTERNAL FACTORS THAT INFLUENCE GROWTH . ; o> dG + 253 
Influence of Food . : . : . . : 3 - 253 
Stimulants affecting Growth . z “ é : : . 256 
Effects of Salton Growth. ire es Ee : : . 257 
Effects of Heat on Growth . ‘ ti ‘i A Z ‘ , . 260 
