12 



GENETIC STUDIES OF RABBITS AND RATS. 



Fi, varies about class 16 as a mode, being about 300 grams lighter 

 in average weight than the FI groups. The variability of this group 

 as measured by the standard deviation is only slightly greater than 

 that of FI, being 233 grams as compared with 218 grams for FI. 



13 14 15 1617 18 19 2)21 ZZZZZ4 25262728 73 3031 323334.35363738334041 

 WEIGHT, IN HEKTOGRAMS 



FIG. 5. Polygons showing variation in weight of pure Polish (P) 

 and pure Flemish (F) rabbits, and of their FI and Fa 

 hybrid offspring. 



Figure 5 shows the effect upon weight of the widest of the three 

 crosses, that between Polish and Flemish. The parental groups 

 are separated by over twenty classes. FI lies midway between them, 

 its mean falling in class 25. The variation polygon is rather flat 

 and wide, which would seem to indicate lack of complete genetic 



uniformity in one or both parent races. 

 F 2 is of similar form, but is shifted about 

 four classes farther to the left. A sim- 

 ilar movement of the mean occurred in 

 the Polish-Himalayan cross between the 

 Ft and the F 2 genera- 

 tions. The variability, as 

 measured by the stand- 

 ard deviation, has in- 

 creased by about 25 per 

 cent, from 198 grams in 

 FI to 257 grams in F 2 . 



Figure 6 shows for 

 the Himalayan-Flemish 

 cross the variability in 



weight of FI and F 2 . FI is strictly intermediate between the 

 parental races. Its mode lies in class 27, but the average is somewhat 

 higher, being 2,827 grams (table 3). The mode of F 2 lies three classes 



NO. 



14- 

 12- 

 10- 

 8- 

 6- 



4- 



2- 

 O 



6 



F 2 ,HXF 



F,,H*F 



H -r, 



15 16 17 18 192021 Z2a3E4aS2627Z629303l 3E33J* 3536373839*0 

 WEIGHT, IN HEKTOGRAMS 



FIG. 6. Polygons showing variation in weight of pure 

 Himalayan (//) and pure Flemish (F) rabbits, 

 and of their FI and Fj hybrid offspring. 



