EYE COLOR AND HAIR COLOR IN MAN. 5 1 



is seen while the h'ghter shades of blue and the coarser grays 

 seem to be due to the greater coarseness and opacity of the same 

 tissues." These tissues "become coarser with..age and young 

 children with dark blue eyes may mature into adults with light 

 blue, blue or gray eyes." 



The various shades from light brown to black .are due to dif- 

 ferent amounts of dark pigment deposited in the iris, blue eyes 

 being those in which dark pigment is absent. Green is produced 

 by a small amount of yellow pigment with blue or black. Yellow 

 pigment, however, is of minor importance compared with the 

 other color factors. Eyes commonly classed as gray may con- 

 tain a small amount of dark pigment with the blue or blue and 

 yellow or they may be due to a fine mottling of green and blue. 

 Eyes are very commonly mottled in various ways, and they are 

 frequently "ringed," the darker color being more dense around 

 the margins of the pupil. 



It is evident that eye colors cannot be divided into sharply de- 

 fined classes. All sorts of intermediate shades occur as well as 

 irregularities in the distribution of pigment over the surface of 

 the iris. Color classes, therefore, are largely arbitrary categories. 

 Perhaps, as the Davenports suggest, the most natural grouping 

 is the one based on the presence or absence of melanin pigment. 

 Black to light brown would fall into one class. Blue and green 

 would fall into another while the grays would be divided between 

 the two. There are, however, all grades in the amount of mela- 

 nin pigment present and whether there are cases in which it does 

 not exist in minute traces may reasonably be questioned. Hurst 

 has divided eyes into the simplex and duplex types ; in the former 

 dark pigment occurs only in the posterior coat of the iris ; in the 

 latter in both coats. As a rule the darker colors belong to the 

 duplex type, the lighter colors to the simplex type. This rela- 

 tion suggests that the difference may be due mainly to the amount 

 of general pigmentation, the amount of pigment when small 

 being deposited in the posterior coat and extending also into the 

 anterior coat only when present in increased quantity. There is 

 nothing which shows that these classes are not the result of a 

 purely continuous series of variations. 



Our results on the inheritance of blue eyes bear out in general 



