MENDELIAN SEGREGATION 13 
istic Mendelian ratio when one pair of characters is 
involved. 
In a third-chromosome stock, ebony, the body and 
wings are very dark in contrast to the wild fly whose 
color is ‘“gray.’’ Gray is used to designate the color 
of the wild fly, whose wings are gray, but whose 
body is yellowish with black bands on the abdomen. 
If ebony is crossed to gray the offspring (F) are gray 
but are somewhat darker than the ordinary wild flies. 
When these hybrids are inbred they give (F.) 1 gray, 
to 2 intermediates, tol ebony. The group of inter- 
mediates in the second generation (F.) can not be 
separated accurately from the pure gray type. If they 
are counted as gray, the result is three grays to one 
ebony. 
Since ebony and gray assort independently of long 
and vestigial, as will be shown later, the factor for 
ebony must be supposed to be carried by a chromo- 
some of a different pair from the one that carries 
vestigial. Since this chromosome behaves in the 
same way as does the one that bears the vestigial 
factor, the scheme used for vestigial will apply here 
also. 
Another mutant stock is characterized by small 
eyes, and since in the extreme form it may lack one 
or both eyes entirely (Fig. 7), the name “eyeless”’ 
has been given to this mutant. When this stock is 
bred to wild flies the offspring have normal eyes. 
These inbred give three normal to one eyeless fly. 
As shown in the table on page 6, this character 
belongs in still another, the fourth, group, and its 
