LOSS OF EYE-PIGMENT IN GAMMARUS. 345 
7. Matings giving normal-eyed offspring of three colours in the proportion 
oo > Ds 
Number of young. 
Black-eyed.  Red-eyed. Albino-eyed. 
B+R+AxR-+A Experiment 235 169 144 
Theory 205 205 137 
It will be noticed that in both this and the preceding instance the pro- 
portion of total coloured (red and black combined) to albino is in good 
agreement with the Mendelian theory. In each case, however, the 
experiment gives a great excess of blacks over reds, whereas theory re- 
quires equality in each case. The numbers are fairly large and it is 
possible that this result may have some significance. 
Section III. Animals occurred in which the chalk-white extra-retinal 
pigment of the eyes was absent. These we have called ‘‘ no-whites.” 
This mutation appeared independently in several different stocks, and 
there is evidence that it may be produced in a series of steps or stages, 
the white pigment being gradually reduced in amount. In some cases 
the two eyes of the same animal differ in respect to the presence or 
absence of white pigment, or in the amount of white pigment. The “ no- 
white ” eye behaves in inheritance as a simple Mendelian recessive to 
the presence of white. 
The following numbers are derived from the experiments made with 
these animals, including also the experiments made with the Albino 
no-whites (AN) or Colourless, described in the next Section. 
1. Matings giving no-white-eyed offspring all of one colour. 
Black, offspring all Black no-white in appearance, in agreement with 
theory. 
Number of young, Black no white. 
BN «BN 13 
BNxRN 13 
Red, offspring all Red no-whites in appearance, in agreement with 
theory. 
Red no-whites. 
RNxRN 61 
RNxAN+R Livi 
Albino, offspring all Albino no-white in appearance, in agreement with 
theory. 
Albino no-whites (i.e. Colourless). 
ANxAN 489 
