PHENOMENA OF INHERITANCE 267 



mediate between the two parents; but when 

 these hybrids were interbred they produced 

 banded, faintly banded and uniformly colored 

 snails in the ratio of 1:2:1, thus proving that 

 Mendelian segregation takes place in the F 2 

 generation, and that dominance is incomplete 

 in the heterozygotes. Many other similar 

 cases of incomplete dominance are known. 



Sometimes dominance is incomplete in early 

 stages of development but becomes complete 

 in adult stages. Davenport found that when 

 pure white and pure black Leghorn fowls are 

 crossed the chicks are speckled white and 

 black, but in the adult fowl dominance is com- 

 plete and the plumage is black. Similar con- 

 ditions of delayed dominance are well known 

 in the color of the hair and eyes of children, 

 though dominance may become complete when 

 they have reached adult life. 



In a few instances a character may be domi- 

 nant at one time and recessive at another. 

 Thus Davenport found that an extra toe in 

 fowls is dominant under certain circumstances 

 and recessive under others. Tennent found 

 that characters which are usually dominant in 



