ILLUSTEATIONS 13 



93. Non-Disjunction. Egg Fertilized by X-Sperm 201 



94. Non-Disjunction. Egg Fertilized by Y-Sperm 202 



95. A Wingless Aphid and a Winged One 207 



96. Curve Showing the Non-effect of Selection for the First Twelve 



Generations for Increase in Body Length 208 



97. Curve Showing the Effect of Selection for the Second Score of 



Generations 209 



98. Scheme Showing Dispermic Fertilization of the Egg of the Sea 



Urchin 214 



99. First Division of a Hybrid Egg 215 



100. Fertilization of an Egg Starting to Develop Parthenogenetically . . . 216 



Larval Sea Urchin Seen in Side View 217 



Green Leaf and Checkered Leaf of Four-o'clock 220 



Pelargonium that Gave Rise to a White Branch 221 



Diagram to Show How a Sectorial Chimera May be Produced 221 



Diagram to Illustrate Maternal Inheritance 228 



Diagram to Show the Inheritance of Two Pairs of Mendelian 



Characters 238 



A, Hen-Feathered Campine Male;B, Adult Castrated Campine Male; 

 C, Sebright Hen-Feathered Male, D, Adult Castrated Sebright Male 246 



Diagram Illustrating Mutation in a Nest of Genes 252 



Two Flies (Drosophila) with Beaded Wings 258 



Diagram Showing the Relation of the Chromosomes 258 



Diagram to Show how the Appearance of a Lethal Near Beaded 



Causes the Stock to Produce only Beaded 259 



Diagram Showing the Results of Crossing Over in a Stock Contain- 

 ing Both Beaded and Lethal 260 



Diagram Illustrating How in the Presence of a Dominant Factor, 

 Dichete, and a Lethal in Its Homologous Chromosome at About 

 the Same Level, Together with Another Factor, Peach-Colored 



Eyes, Gives the Result Shown in the Squares 261 



Diagram Illustrating Crossing Over of Factors in Fig. 113 262 



Rosettes of the Twin Hybrids of the Evening Primrose 263 



Diagram Illustrating Balanced Lethals and Twin Hybrids 264 



Diagram Illustrating Lethals and Four Types 265 



