368 Eiger dig AU ne Ni 
one investigating problems of inheritance, because its result enables us to 
distinguish the pure dominant from the hybrid which in appearance 
resembles it. We have seen that the pure black mated with red gives all 
black offspring. H, therefore, when a black and a red are mated together 
we get some red-eyes amongst the children, we know that it is a hybrid 
black that we are dealing with. 
One other mating of these two varieties remains to be considered. 
When hybrid blacks are mated with pure blacks, the dominant asserts 
itself completely, and all the offspring are black-eyed. The total number 
of young obtained in our earlier experiments from crosses of this kind was 
379—all with black eyes. 
In one family, belonging to the first generation of hybrids got by cross- 
ing the red-eyed Gammarus with the pure black-eyed one, a second sport 
j EYE 
FROM 
SIMILAR 
FAMILY 
4n4aandenénaad 
a a | 
DIAGRAM 7. 
A Black dise with white centre represents a black-eyed animal. 
A Black dise with white cross represents a red-eyed animal. 
A Black ring represents an albino-eyed animal. 
$=male. 9 =female. 
or mutation appeared. The brood in which this mutation occurred con- 
sisted of 7 black-eyed young, | red-eyed and 4 in which neither black nor 
red pigment could be seen, and only the network of chalk-white pigment 
was left. (Plate VII, Fig. 4, of preceding paper.) The eye was also very 
irregular in shape and altogether of a degenerate character, the number 
of ommatidia being very few. These degenerate eyes, with only white 
pigment, we shall speak of as “ albino ” eyes. 
In order to determine the constitution of these degenerate albino eyes, 
and to find out whether or not the condition was hereditary, one of the 
animals, a female, was mated first with a pure red male, and then with a 
known hybrid black one. 
The result of these matings is shown on Diagram 7, and will probably 
