SIZE. 



53 



THE ICA HYBRIDS. 



Crosses with the lea race were made principally by a male of race C 

 whose measurements are known and which slightly exceed the averages 

 for race B males; but a few crosses with the lea race were also made with 

 race B females (mated with lea males). The measurements given in 

 table 32 for the mates of the lea race are a mean between the meas- 

 urements of races B and C. The standard deviation of the mixed 

 parents should of course exceed that of race B alone, which should 

 increase the variability of F-i and F 2 , but should not alter the relative 

 variability of these two, since the race B and race C hybrids were bred 



TABLE 32. Statistical constants derived from tables 23 to 25. 



entirely distinct from each other and are only tabulated together to 

 secure greater numbers. Again in this cross we are confronted with the 

 same phenomena as regards the skeletal measurements: (1) in F! a 

 substantial increase in size (least in skull length of FI male hybrids) ; 



(2) while in F 2 a return is made toward the mid-parental (mean of the 

 races crossed), in 4 of the 6 measurements it is closely approximated; 



(3) the standard deviation meanwhile alters little, not enough to have 

 significance ; the lea crosses are of particular interest because the races 

 mated are of nearly the same size. The phenomenon of increased size 

 in F! followed by a prompt loss of the increase in F 2 is here observed 



