SIZE INHERITANCE 191 



as a tendency toward segregation of the original types. 

 These, the well established facts, were at one time regarded 

 as showing the occurrence of a distinct type of inheritance 

 known as blending, but at present we are inclined to give 

 them a different explanation, the same in fact as for ordinar\" 

 Mendelian inheritance except that several factors, instead of 

 one, are supposed to be concerned in the case, and that 

 dominance is not in evidence. 



If a large rabbit is crossed with a small one, the young are 

 of intermediate size and the F2 offspring show no such segre- 

 gation into large, small, and intermediate-sized individuals 

 as a simple Mendelian system would demand. For if tlie 

 size difference between a large and a small rabbit depended 

 upon one unit-character, then the F2 animals should be as 

 regards size in the proportions, one large, two intennediate, 

 one small. But in the cases thus far studied all F2 individ- 

 uals are intermediate in size. A specific case illustrating the 

 point is the following: A cross was made between a large lop- 

 eared rabbit and a small short-eared one. The fonner was 

 also a sooty yellow animal and short-haired (Fig. 127); the 

 latter an albino and long-haired (angora). See Fig. 126. The 

 character of Fi is shown in Fig. 128. Notice first the smiple 

 Mendelian behavior of the color characters and the hair- 

 length. Albinism disappeared in Fi, for all the Fi aninuils 

 were black. But it reappeared in Fo; one Fo albino is shown 

 in Fig. 129. Long hair also behaved as a Mendelian recessive 

 (as in guinea-pigs), disappearing in Fi but reappearing in F- 

 as expected, sometimes in colored individuals, sometimes in 

 albinos, thus showing its independent inheritance. The 

 black character seen in the Fi individuals was received from 

 the albino (angora) parent, which had black ears. The black 

 character (dominant in Fi) was found in a majority of the 

 F2 colored individuals also, as we should expect, but the 

 yellow character of the other grandparent reappeared as a 

 recessive in F2 in certain of the individuals. Three inde- 

 pendent coat characters were thus Mendelizing in the cross, 

 viz.. 



