a 
LOSS OF EYE-PIGMENT IN GAMMARUS. 335 
that the first brood of grandchildren got by mating together two black- 
eyed children of the cross albino by red no-white, consisted of two normal 
black-eyed animals, one black no-white, and two quite colourless. Since 
then a number of others with colourless eyes have been bred. The full 
details of the experiments made may now be given. 
Parent Generation. 
1. Albino carrying black and red mated with Red No-white (A+-B-+-R « 
RN). 
A mating of this kind is illustrated on Plate III, Fig. 6, where the male + 
(II.D.1.j.) is Albino and the female “ No-white ” (from Family K, Plate 
V). Eighty young were obtained of which 42 were normal black-eyed 
animals and 38 normal red-eyed. 
Another mating of this kind gave 34 young, 17 normal black-eyed and 
17 typical red-eyed young. 
2. Albino carrying black mated with Red No-white (A+B x RN). 
The male IT.D.1.k. (Plate IJ) was mated with a female red ‘*‘ No-white ”’ 
from Family VII (Plate V) and gave 38 young, all being normal black- 
eyed animals. (Two of these 38 young which were mated together gave 
in the first brood 1 colourless young one, which is referred to as C.27, 
p. 338.) 
From several matings of this kind including the one mentioned a total 
of 158 young was obtained, all normal black-eyed animals. One of 
these matings is illustrated in Plate IV, Fig. 17 (ef. p. 349). 
3. Albino carrying red mated with Red No-white (A+R x RN). 
From the matings of this kind there resulted 137 young, all typical 
red-eyed animals. 
F.1\. Generation from A+B+Rx RN. 
Three typical experiments are illustrated on Plate VI, Figs. 1, 2 and 3, 
the ancestry of the animals used being shown on Plate III, Fig. 6. 
Black with Black. 
Fig. 1 (Plate VI) shows the result of mating together two black 
offspring (Plate III, Fig. 6, I1.D.1.j.2.) of Albino carrying black and red 
crossed with Red No-white (see Parent generation above, Section I). 
The first five broods given in the figure consisted of 80 young. 
The numbers of each category required by the theory (see p. 332) for 
80 young are given below, and those actually obtained are placed beneath 
them :— 
