MULTIPLE FACTORS 233 
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 
nd 
Le 
ey 
Back cross 
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Fz 
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Fig. 57.—lllustrating the results of a cross between pigeons with 12 
tail feathers and a raee of fantail pigeons with from 28 to 38 tail feathers. 
The number of feathers in Pi, Fi, F2, and the offspring of the backcross 
(F, by fan tail) is given. In each case the numbers on the base line stand 
for tail feathers. The vertical rows are the classes. 
twelve tail feathers; the fantails used in the cross 
have from 28 to 38 tail feathers. The F, hybrids 
(41 birds) have from 12 to 20 tail feathers; the F, 
have 12 to. 25 in a count of 67 birds. When the Fi 
