xii LIST OF ILLUSTRATIONS 



PAGE 



Fig. 43. A Case of Autosite-Parasite Chick Twins in the 



Making 87 



Fig. 44. Types of Frog Twins 92 



Fig. 45. Double Monster Turtle (Anadidymus) .... 95 



Fig. 46. Early Stage of Twinning in the Armadillo . . 109 



Fig. 47. A Little Later Stage of Twinning in the Armadillo 114 



Fig. 48. Polar View of Armadillo Quadruplet Blastoderms . 115 



Fig. 49. Diagram Showing Streeter's Conception of the 



Mode of Twin Formation in Man .... 128 



Fig. 50. Common Placenta and Hearts of a Pair of One-Egg 



Human Twins . 144 



Fig. 51. Common Placenta of Another Pair of One-Egg 



Human Twins 145 



Fig. 52. Example of acardius acormus 152 



Fig. 53. Example of acardius acephalus 153 



Fig. 54. Example of acardius amorphus 154 



Fig. 55. Human Anadidymus 166 



Fig. 56. Viscera of Foregoing Anadidymus Showing situs 



inversus viscerum 167 



Fig. 57. Horizontal Section through Head of Trout Ana- 

 didymus 168 



Fig. 58. Skull Structure of Trout Anadidymus .... 169 



Figs. 59-61. Various Degrees of Heart Doubling in Trout 



Twins 170 



Fig. 62. Trout Anadidymus Showing situs inversus viscerum 172 



Fig. 63. Double-Monster Trout of Autosite-Parasite Type, 



Showing Partial situs inversus viscerum . . 173 



Fig. 64. Bipennaria Larva of Patiria with Bilaterally Sym- 

 metrical Hydrocoele Derivatives 181 



Fig. 65. Pluteus Larva of Echinus miliaris Showing Reversed 



Asymmetry of Hydrocoele Derivatives . . . 184 



Fig. 66. Example of Limb Duphcity in an Insect . . . 193 



Fig. 67. Diagram of Limb Reduplication in AmUystoma . 199 



Figs. 68-7 1 . Various Degrees of DupUcity of the Human Hand 202 



