LIST OF ILLUSTRATIONS xi 



no. 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 G6 



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



37. — A silvered guinea-pig Facing 101 



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



JB. 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 jD 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 Fa descendant of the rabbits shown in 



Figs. 44 and 45 Faxing 132 



