IN RATS AND GUINEA-PIGS. 



50 



+0 



35 



30 



SO 



AS 



fO 



\ 



\ 



\ 



60 



50 



4O 



35 



20 



/5 



\ A 



\ 



\ 



\ 



345 44.5 



54.5 



64. 5 74.5 



Grade 4.5 /4.5 



FIG. 3. Variation in extent of the back-stripe in lots A to F of hooded rats, showing the effects of cross- 

 breeding with rats of Irish pattern. The positions of the means are shown by vertical lines. 



