SIZE CHARACTERS SEEMING TO " BLEND." 23 



intermediates. The largest number of individuals from one pair of 

 parents was 12; there were two fraternities of 9, while the average size 

 of the thirty-five fraternities reported was 5.2 individuals. On the 

 supposition that size differences are due to the presence of two or more 

 similar independent activities, it would be impossible to find a marked 

 difference in the variability of first and second generation fraternities 

 consisting of five animals. If an intermediate Fi animal from a cross 

 involving three factor-differences for a size character be crossed back 

 to one parent, there would be six intermediates to one like each parent. 

 It is notable that with two of the largest fraternities given by Castle 

 the variability is unusually wide. It is indicated that this variability is 

 no greater than that found in the largest family of lops bred inter se. 

 Three of these five lop-eared rabbits lie between their parents. The 

 width of the range is then determined by two individuals. The curves 

 plotted for these animals (Castle 1909, fig. 2, p. 13) show that at four- 

 teen weeks one of these low animals had an illness, or was set back in 

 some way, and at twenty weeks, when the records stop, it had not 

 made up for this loss. The curves for ear growth and weight show the 

 same thing. The second low animal at two weeks was only half as 

 large as the other four, all of which were about the same size at that 

 time. It has been found true of rabbits, as was noted in the case of 

 cotton plants (Balls 1907) that the differences in size do not appear 

 till several weeks after the birth. This means that normal curves of 

 a litter would begin together and then fan out. (Compare curves given 

 by Castle 1909, fig. 1, p. 11, and fig. 3, p. 15.) The curve of the rabbit 

 in question remains below the others in that litter. In all probability 

 this animal was set back seriously when first born and in fourteen weeks 

 did not fully make up for it. Comparing the fraternity of twelve with 

 the fraternities from short-eared rabbits bred inter se, and comparing 

 it with the largest F x fraternities, its variability takes on a new light. 



Since the appearance of Nilsson-Ehle's paper, Lang (1910), Baur 

 (19106), and Castle (1911), himself, have presented discussions of the 

 possibility of finding increased variability in ear length in the second 

 generation, among larger numbers of rabbits. 



