R. C. PUNNETT AND P. Gr. BaiLEY 20 



In Fig. 1 the F^ weights at intervals of 50 grams have been 

 arranged to give the curves of variation \ For each sex these curves 

 are irregular. Probably they cannot be regarded as simple curves of 

 error, but appear rather to suggest that we are dealing in either instance 

 with compound curves made up of several simple ones. Further 

 analysis however must come from the breeding pen, and in this direc- 

 tion we have already taken the first step with some experiments in 

 raising a further generation from certain of the F. birds. 



Tlie F3 generation. It was clear that the first step towards analysing 

 the F., birds was to test whether the largest and the smallest bred true. 

 With this purpose three pens of F^ birds were mated up in 1913, viz. a 

 pair of the largest birds and two jaairs from among the smallest. 



(A) For the pen of larger birds we selected an F. hen (PI. IV, fig. 6) 

 which was more than 100 grams heavier than any other F.. $ yet bred. 

 Her weight at 35 weeks was 1290 grams. The F„ ^ chosen (PI. IV, fig. 

 5) weighed 1390 grams at the same age, and was among the heaviest 

 of the 1912 birds. (In 1913, however, we bred two heavier F„ cockerels.) 

 From this mating 13 (/(/ and 13 $ $ were reared during the past 

 season. The </(/ ranged between 990 and 1630 grams, averaging 

 1360 grams, while the % % were between 930 and 1350, averaging 

 1150 grams. The offspring of the large F^_ birds must all be reckoned 

 on large side, though they showed a good deal of variation. Nothing 

 approaching a bantam was jjroduced by these two birds. 



(B) Of the two pens of small F„ birds put up in 1913 one (Pen 13) 

 consisted of a pair of the smallest F« birds reared by us. The </ (PI. IV, 

 fig. 5) weighed 680 grams and the % (PI. IV, fig. 6) but 540 grams. These 

 figures are rather below the average weights of the original Sebrights. 

 Unfortunately the hen died before she had laid many eggs and we only 

 reared five birds from her. Of these 2 were ^^ and 3 were % % , and 

 all of them were below 600 grams. 



(C) The other pair of small F„ birds was rather larger than that 

 just discu.ssed. Here (Pen 7, 1913) the </ weighed 740 and the ^ 

 710 grams. She must probably be regarded as belonging to the 

 smaller of the intermediates, rather than as pure extracted bantam. 



' The curves for the two years 1!)12 and 11113 have been given separately. The 

 average weight of the birds in the latter year is somewhat lower than in the earlier one. 

 This is due to an outbreak of diphtheritic roup which affected about half of the F^ birds 

 in 1913. Many of these birds had probably not recovered their normal weight when killed 

 at the age of 35 weeks. 



