FIG. 36. An imperfectly rough guinea-pig. Produced by mating 

 the guinea-pig, shown in Fig. 32, with a particular smooth animal; 

 female, 2005. 



FIG. 37. A silvered guinea-pig. One in whose coat occur white 

 hairs interspersed with pigmented ones. The amount of the silver- 

 ing has been greatly increased by selection. 



FIG. 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 con- 

 dition of the hind feet of young obtained by crossing B with D. 



FIG. 39. Diagram showing variation in the color-pattern of hooded 

 rats. 



