Illustrations 15 



PAGE 



84 Canadian and transition zone landscape 174 



85 Beaver 175 



86 Beaver pond 176 



87 Cypress swamp 177 



88 Cotton rat 178 



89 Alligator 179 



90 Water moccasin 179 



91 Burrowing owl 180 



92 Prairie dog . . 181 



93 Prairie dog at burrow 181 



94 Horned toad 183 



95 Kangaroo rat 183 



6 Gila monster '.'.'.:. 184 



97 California big trees :,. 185 



98 Mountain beaver 186 



99 Beroe 189 



100 Organ-forming substances in the egg 190 



101 Four-legged tadpoles 195 



102 Combination frog 196 



103 Reconstruction of wounded soldier's face 198 



104 A piece of growing tissue 199 



105 Mitosis in a sea urchin's egg, showing chromosomes .... 204 



106 Diagram of inheritance of size in sweet peas 205 



107 Diagram of combinations of three pairs of chromosomes . 206 



108 Photographs of chromosomes, showing sex chromosomes . . 208 



109 Gynandromorph fruit flies 209 



110 Diagrams showing distribution of sex chromosomes in ma- 



turation 211 



111 Fruit flies, showing mutations 212 



112 Diagrams showing chromosomes in relation to sex linkage . 213 



113 Chromosome map showing distribution of linked characters 



in the fruit fly 216 



114 Diagrams of chromosomes in the fruit fly showing result of 



non-disjunction 217 



115 Influence of environment on plants 221 



116 Effect of diet on body form in Amblystoma ....... 225 



117 Scarlet tanager and bobolink, showing sex differences . . . 226 



118 Cyclopean fish 228 



119 Human twin monster 229 



120 Types of human faces 229 



121 A human monster 230 



122 Moulted skin and egg case of daphnid 231 



123 Diagram showing pure lines in beans 237 



124 Hooded rats 238 



125 Mutation in (Enothera 239 



126 A rumpless fowl .240 



127 Diagram showing height variation in man 241 



