x LIST OF ILLUSTRATIONS 



FIG. PAGE 



17. A group of four young, produced by the 



animals shown in Fig. 16 ... .Facing 34 



18. Diagram to explain the result shown in Fig. 17 35 



19. A shortened condition of the skeleton, par- 



ticularly of the fingers Facing 36 



20. Radiograph of a hand similar to those shown 



in Fig. 19 Facing 38 



21. Diagram showing the descent, through five 

 generations, of the condition shown in 



Figs. 19 and 20 40 



22. A smooth, dark guinea-pig ..... Facing 40 



23. A rough, white guinea-pig Facing 40 



24. A dark, rough guinea-pig Facing 40 



25. A smooth, white guinea-pig Facing 42 



26. A short-haired, pigmented guinea-pig Facing 42 



27. A long-haired albino guinea-pig . . . Facing 42 



28. Offspring produced by animals of the sorts 



shown in Figs. 26 and 27 ... .Facing 42 



29. A long-haired, pigmented guinea-pig, "Dutch- 



marked " with white Facing 42 



30. Diagram to explain the results of a cross 



between the sorts of guinea-pigs shown in 

 Figs. 26 and 27 43 



31. Diagram showing the kinds and relative 



frequencies of the young to be expected in 

 F 2 from the crossing of animals shown in 

 Figs. 26 and 27 46 



32. Along-haired, rough albino guinea- pig Facing 46 



33. Five new combinations of unit-characters 



obtained in generation F 2 , by crossing the 

 animal shown in Fig. 32 with animals like 

 that shown in Fig. 22 . , , . . , Facing 48 



