X ILLUSTRATIONS 



44. Chromosomes and genes in a single factor 



cross 209 



45. Ratios produced when parents differ in two 



gene pairs 213 



46. Inheritance of recessive characters that are 



alleles 220 



47. Inheritance of recessive characters that are 



not alleles 221 



48. Axolotl and Amblystoma 240 



49. Abnormal abdomen in Drosophila 242 



50. Reduplicated legs in Drosophila 243 



51. Mating of darker and lighter Salamandra 251 



52. Sea urchin egg fertilized by mollusk sperm 268 



53. Results of crossing different genera of sea 



urchins 271 



54. Lagging behind of male nucleus and chro- 



mosomes in eggs of Sphaerechinus 272 



55. Germ cell formation in the mule 274 



56. Development of a hybrid 277 



57. Result of a cross between long-legged and 



short-legged dogs 279 



58. Hybrid between a Great St. Bernard dog and 



a Dachshund 280 



