LIST OF ILLUSTRATIONS xt 



FIG. PAGE 



34. Diagram to show the gametic combinations 



and segregations involved in a cross be- 

 tween guinea-pigs differing in three unit- 

 characters 49 



35. Diagram to show the gametic combination 



and recombinations which occur in the 

 production and fixation of an atavistic coat- 

 character in guinea-pigs 66 



36. An imperfectly rough guinea-pig . . .Facing 101 



37. A silvered guinea-pig Facing 101 



38. A. Front feet of an ordinary guinea-pig. 



B. Its hind feet D. Hind feet of a race 

 four- toed on all the feet. C. Ordinary 

 condition of the hind feet of young obtained 

 by crossing B with D Facing 101 



39. Diagram showing variation in the color- 



pattern of hooded rats Facing 101 



40. Diagram showing the variations in size of 



eight different races of paramecium ... 112 



41. Chart showing effects of selection in eight 



successive generations upon the color- 

 pattern of hooded rats 122 



42. Skulls of three rabbits Facing 128 



43. A long-haired, albino rabbit, having erect 



ears Facing 132 



44. A short-haired, sooty yellow rabbit, having 



lop ears Facing 132 



45. A short-haired, black rabbit, son of the 



rabbits shown in Figs. 43 and 44 . .Facing 132 



46. An F 2 descendant of the rabbits shown in 



Figs. 44 and 45 .,,.,,., .Facing 132 



