xviii LIST OF ILLUSTRATIONS 



PAGE 



79. Diagram Illustrating Complementary Factors .... 418 



80. Diagram Illustrating Behavior of Inhibitory Factor . . 421 



81. Diagram Showing Some Possible Combinations in F^ When 



Fi OF Figure 80 Is Inbred 422 



82. Diagram Showing the Heterozygote Situation . . . . 422 



83. Diagram Illustrating the Action of a Supplementary 



Factor 423 



84. Diagram Illustrating Nilsson-Ehle's Explanation of the 



15:1 Ratio in Fj of Hybrid between Red- and White- 

 grained Wheat 425 



85. Another Method of Visualizing Nilsson-Ehle's 15:1 Ratio 426 



86. Dl^gram of Nilsson-Ehle's 63 : i Ratio 427 



87. Sex-Linked Inheritance of White and Red Eyes in Droso- 



phila 434 



88. Reciprocal Cross to That Shown in Figure 87 . . . .435 

 8g. Drawing Sho\\7ng the Four Pairs of Chromosomes Seen in 



THE Dividing Egg of Drosophila 436 



90. Diagram Showing the Location in the Four Paired Chromo- 



somes of Drosophila, of the Genes for Various Mendeliz- 

 ING Characters, as Determined by Morgan 437 



91. Sex-Linked Inheritance of Barred and Unbarred (Black) 



Plumage in Poultry 438 



92. Reciprocal Cross to That SHO^VN in Figure 91 ... . 439 



93. Diagram to Show the Mechanism of Crossing Over . . . 440 



94. An Armadillo Egg about Six Weeks after Fertilization, 



Showing the Quadruplet Foetuses 451 



95. A Typical Opposite-Sexed Pair of Cattle Twtns .... 455 



96. A Pedigree of Brachydactylism 460 



97. A Pedigree Showing Transmission of Cataract .... 461 



98. A Pedigree Showing Heredity of Feeble-Mindedness . . 463 



99. Another Pedigree Showing Heredity of Feeble-Minded- 



ness 464 



100. Pedigree Showing Heredity of Insanity 465 



loi. Pedigree Showing Heredity of Insanity and Neurotic 



Tendency 465 



