186 



MULTIPLE FACTORS 



A race of pigeons called fantails differs from other 

 pigeons, and from birds in general, by the large num- 

 ber of feathers in the tail. The ordinary pigeons have 



! 



;. 



L. 



FIG. 57. Illustrating the results of a cross between pigeons with 12 

 tail feathers and a race of fantail pigeons with from 28 to 38 tail feathers. 

 The number of feathers in Pi, Fi, F2, and the offspring of the backcross 

 (Fi by fantail) is given. In each case the numbers on the base line stand 

 for tail feathers. The vertical columns are the classes. 



twelve tail feathers; the fantails used in the cross 

 have from 28 to 38 tail feathers. The Fi hybrids 

 (Fig. 57) have from 12 to 20 tail feathers; the F 2 have 

 12 to 25 as also shown in figure 57. When the FI 



