R C. PUNNBTT ANDTHK LATK P. O. BaILKV 17 



compared with the buck. That thin factor (or factont) may be tranH- 

 iiiitt<?<i by the buck appiMirH pn)l)abK* fnmi th<* rfHullH obUiint><l fn»u» 

 J A^230. With two brnthcn* of alinoMt exactly the kiuih' wei^'ht, N 2'M\ 

 and 041, she gave in one cjwe a family in which the pniiiindcnitHM; of 

 weight wjus rather on the side of the bucks and in the <)th<'reji«<' u family 

 in which the doe» wen* markedly heavier. That the fiu'tor (or factorM) 

 may also be transmittiMi by the <loe is indiaited by the rcHultM of the 

 Flemish- Polish cn^sses. With the same Polish (/* the heavier FleinJMh 

 doe (0 138) gave rise to an F^ generation when; the inarke<l di.Hcrejwinry 

 in weight between the sexes apjx'ari'd, while with a lighter Flemish J 

 (0203) the Ft generation shewe<I little dift'erence in the average? weight 

 of the bucks and does. So far jus they go, the dat;i suggest the o|>era- 

 tion of a factor which leads to an incre^ise in the weight of the doe that 

 contains it, though not at all, or only to a slight extent, in that of the 

 buck. Much more work however must be done before we am arrive at 

 certainty on this point, but there seems little doubt but that it is a 

 complication which must be borne in mind in work dealing with the 

 inheritance of weight in this species, and possibly of others also. 



B. Rate of Growth. A marked difference in the rate of growth 

 between the two sexes has long been recognised in man where stiitistics 

 bearing upon the point are more plentiful than in other animals. Up to 

 about 13 years of age the female grows rather more rapidly than the male. 

 After this point the male overtakes the female and eventually becomes 

 markedly heavier^ This differential growth is probably connected with 

 the earlier onset of puberty in the female sex. Our records allow of 

 some examination of this point in the rabbit, and we have prepared the 

 following brief abstract (Table B) from the data given in Tables II-V 



TABLE B. 



Males Females 



^ According to Darwin (Descent of Man, 1891, p. 283) a fiimilar differential sex K'ruwth 

 is found in the Scotch deer-hound. 



' Under this heading the figure in front of the dtciiual point denotes pounds while 

 the figure or figures after it denote ounces — e.g. 312 is to be read as 3 lbs. 12 oz. 

 Joum. of Gen. viii 2 



