CONTENTS 



PAGE 



List of Illustrations xi 



CHAPTER 



I. The Nature, Scope, and Causes of Twinning . i 



II. Experimental Production of Twins in Starfishes ii 



III. Twinning in Earthworms and Their Allies . . 28 



IV. One-Egg Twins in Fishes 38 



V. Double Monsters or Conjoined Twins in Fishes 51 



VI. Twinning in Birds 73 



VII. Twinning in Amphibia, Reptiles, and Other 



Chordates 91 



VIII. The Causes of Twinning in the Armadillos . . 100 



IX. The Modes and Causes of Human Twinning . . 121 



X. Developmental Hazards of Human Twins . . 135 



XI. Hemihypertrophy — ^A Type of Minimal Twinning 



IN Man 159 



XII. Symmetry Reversal and Mirror-imaging in 



Twins and Double Monsters 164 



XIII. Double Tails in Vertebrates 190 



XIV. Twinning (Duplicity) in Limbs 193 



XV. Twinning as a Mode of Reproduction . . . 206 



Bibliography 220 



Index 229 



3T827 



