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. 



NO. 



20-1 



18- 



16- 



14- 



12- 



10- 



8- 



6- 



4- 



2- 



O-l 



6-1 



4- 



2- 







e-, 



6- 

 4- 

 2 

 



Fp.PXF 



V/.l'/JI/ ^/. 



II 12 13 14 15 16 17 18 19 2021 22 23 24 2526^7 28 29 3031 323334353637 3839 4041 

 WEIGHT, IN HEKTOGRAMS 



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

 and pure Flemish (F) rabbits, and of their Fi and Fj 

 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. 

 F2 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 

 Fi and the F2 genera- 



NO. 

 >6-i 



12- 

 10- 

 8- 

 6- 



4.' 

 2' 

 O 



I 



JU 



F2,HXF 



Fi.HxF 



-^-uzzLm. 



7T\ F7a 



m. 



_EZ3 



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 F2. 



Figure 6 shows for 



the Himalayan-Flemish 



cross the variability in 



weight of Fi and F2. 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 Fj lies three classes 



15 16 17 18 19 20 ZJ 22 23 24 25 26 27 2829 30 31 32 3334 353637 3839*0 

 WEIGHT, IN HEKTOGRAMS 



Fio. 6. — Polygons shov. ing variation in weight of pure 

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

 and of their Fi and Fj hybrid offspring. 



