18 Genetic Studies In Rabbits 



(pp. 22 — 25). The average weights at 4 months and at 12 months^ are 

 given separately for the two sexes from matings in which 12 or more 

 offspring were reared. It is evident that up to the age of 4 months 

 there is little difference between the sexes. Where the sexes eventually 

 attain approximately the same weight (e.g. ex 223 x 222), or where 

 the male is slightly heavier (e.g. ex iV230 x 041), the weight of the 

 female at 4 months is below that of the male. Where, as in most of the 

 other cases, the female eventually reaches a markedly higher weight she 

 is rather heavier at 4 months. But in all cases the growth subsequent 

 to 4 months is greater in the feaiale than in the male. This is brought 

 out in the last column which shows the proportion of the weight at 

 4 months that is added between 4 and 12 months. In every mating 

 this proportion is higher in the case of the does. 



A point of interest brought out in Table B is that the greater the 

 weight to which the animals eventually attain the greater appears to be 

 the proportional increment added after 4 months, for there is not much 

 difference at 4 months between the larger and the smaller animals in 

 the Flemish-mixed series of experiments. The data, so far as they go, 

 suggest that it might be more economical to breed a larger number of 

 smaller rabbits for killing at about 4 months than to. rear a smaller 

 number of larger ones. The latter would have to be kept more than 

 twice as long to gain the advantage of their greater size, and even then 

 the total weight would be less than double that of an equal number of 

 smaller ones killed at 4 months. 



The results of the Flemish-Polish cross offer an interesting contrast 

 to those of the Flemish-mixed cross. Though the F^ animals are all on 

 the small side they are on the whole late in maturing (cf. p. 11). There 

 is practically no difference between the sexes either at 4 months or at 

 maturity which occurs at various ages between 8 and 12 months 

 This applies only to the F^ animals from $ 203. Full records of the 

 smaller F^ generation ex % 138 are not available. 



One further point of difference in growth between the sexes is 

 brought out by an examination of the F^ records. It concerns the 

 extent to which the heavier and lighter animals in such a mixture can 

 be distinguished at a relatively early age ; or, to put it in another way, 

 how far the animals heavier at maturity give evidence of this at the age 



1 The animals were generally weighed at intervals of a month. Since the litters were 

 produced irregularly the weight at 4 months sometimes refers to animals a little over and 

 sometimes a little under this age. Members of the same litter were of course always 

 weighed at the same age. Weight at 12 months means maximum attained by 12 months. 



