LOSS OF EYE-PIGMENT IN GAMMARUS. 329 
above, from wild stock which had not been crossed with red-eved 
animals. 
From a number of animals brought in from Chelson Meadow on Feb 
ruary 11, 1915, certain pairs already mated in the open were put in 
separate finger-bowls. In the descendants of two of these pairs, no-white 
eyes have occurred. The pairs and their offspring will be considered 
separately. 
(1) Pair V. In this pair the female had the white pigment very much 
reduced, the reticulation was perfect but the lines of white were very 
thin and thread-like. She was mated with a normal-eyed male, and had 
a fairly large brood which was not examined when young. Of this brood 
four reached maturity, three males and one female. One of the males 
mated with the female. The eyes of this male were examined and the 
white reticulation though perfect was so thin that it required micro- 
scopical examination with a l-inch power to trace it. The eyes of the 
female were not examined, the male having devoured her alter the 
extrusion of the brood. The brood numbered 13; 5 had a white reticula- 
tion which could just be seen under a hand-lens ; 6 had eyes like the male 
parent, in which the reticulation could only be seen with a microscope ; 
2 had no reticulation and were typical no-whites. All the individuals 
of this brood were left together in the same finger-bowl, where they re- 
mained for some months. At the end of the time 6 very small voung 
were found, all the other animals having died as the conditions in the 
bowl had become unhealthy. Of the 6 young ones, three had no-white 
eyes on both sides, one had no-white on the left side and very faintly 
marked reticulation on the right. The other two were quite normal in 
appearance. One of the no-whites, a female, was mated with male 
III.J. (p. 280). 
For the mating of the one-sided no-white female see p. 340. 
The male referred to above, with very thin white reticulation in the 
eye, was also mated with a normal red-eyed female. There were 47 
black-eyed young, in 45 of these the white reticulation was very much 
reduced, varying from complete but very thin lines to a few scattered 
flecks of white, and in many cases more reduced in the eye of one side 
than in that of the other. In the other two of the 47 young ones the white 
was completely absent from the eyes of both sides. This result is un- 
expected because the reduction of the white pigment appears to be 
dominant over normal white pigment, whereas the absence of white 
pigment has in other cases always behaved as a recessive. 
(2) Pair IV. The parents had normal black eyes, and gave 66 young. 
all normal. These young were left together for six months, and the 
vessel in which they were living then contained 28 survivors, three large 
