1 84 



THE BIOLOGY OF TWINS 



Germinal vesicle of armadillo egg, 



34. 



Germ-layer inversion, 42, 108. 



Hereditary control, limits of, 6, 

 175- 



Heredity: in armadillo quad- 

 ruplets, 125-55; in human 

 twins, 155-69; of double bands, 

 133-45; of double scutes, 145- 

 49; of numbers of scutes, 145- 

 49; versus environment, 169. 



Hermaphrodite, 96, 97. 



Heterosexual, 2, 100. 



Homosexual, 2, 100. 



Inner-cell mass, 40. 



Inversion of germ layers, 42, 108. 



Litomastix, 112. 



Marsupial cat {Dasyurus), 42. 

 Mataco {Tolypeutes), 83. 

 Mirror-image (mirror-imaging), 4, 



17, 152-55- 

 Mon-amniotic, 23. 

 Monozygotic, 3,6. 



Monsters: cyclopic, 5; double, 



4,8. 



Mulita {Dasypus hybrldus), 27, 

 65, 68. 



Multiple births, 4, 113. 



Ovocyte of armadillo, t,^. 

 Ovogenesis of armadillo, 32-35. 



Pairing: exceptions to pairing in 

 armadillo quadruplets, 62; of 

 embryos in same, 58. 



Parasite (?) of armadillo egg, 86. 



Parthenogenesis in armadillo egg, 

 30, 36. 



Peludo {Euphractus viUosus), 77- 

 83. 



Placenta: the development of in 

 Dasypus, 66; discoid of Dasy- 

 pus, 58-60; primitive (Trager) 



of Dasypus, 44; secondary of 

 Dasypus, 56. 



Placentation area, 31. 



Polarity : reversal of, in armadillo 

 ovocyte, 35. 



Polyembr>'ony : in hymenoptera, 

 112; specific, 3, 25, 39, 84; the- 

 ories of, 85-92. 



Putorius (ferret), 91. 



Quadruplets: armadillo, 3, 4, 

 53, 60, 63, 171; human, 3, 114. 



Quiescence, period of, 39, 86. 



Reversal: of polarity in arma- 

 dillo ovocyte, 35; of primary 

 axis of armadillo egg, 44; of 

 symmetry in armadillo quad- 

 ruplets, 141, 145, 148, 153, .154; 

 of symmetry in human duplicate 

 twins, 15, 154, 159, 160, 164, 

 165. 



Sex: determination of, 6, no, in, 

 112; differentiation of, no, 

 116, 117; ratios in twins and 

 multiple births, 10, no, 113, 



115- 

 Somatic segregation, 149-52, 174- 



77.. 



Tatu (Dasypus), 25. 



Tatusia (Dasypus), 25. 



Tolypeutes, 28, 83. 



Trager, 45-54- 



Trager cavity, 69. 



Triplets: human, 3; calves, 108. 



Trophoblast, 40, 43, 44. 



Twinning: blastotomy theory of, 

 16, 17, 89; budding theory of, 

 73, 89; fission theory of, 92; 

 hereditary twinning, 118-20. 



Twins: autosite and parasite, 18; 

 brain convolutions of, 166; 

 conjoined, 3, 5, 8, 18, 20; 

 craniopagi, 19; dizygotic, 15; 

 double monsters, 3, 9, 14, 21; 



