LOSS OF EYE-PIGMENT IN GAMMARUS. 341 
then found that the Right eye had developed the normal white reticula- 
tion, and the left eye had the upper half with the white reticulation, the 
lower half no-white. Mated with a Red no-white male, it had 64 offspring 
B+R-+N 31 and R+N 33, all with normal eyes. 
Two pairs of these have produced young; the first pair, Black with 
Red, had 83 young, 45 Black, 4 Black no-white, 24 Red, 10 Red no- 
white ; and the second pair, Red (R+N) with Red (R+N), gave 53 
young, 39 Red, 14 Red no-white, none showing any variation from the 
normal types. 
These Red F, young are now mature, and their matings Red no-white 
by Red no-white have given 13 Red no-white, and Red (R+N) by Red 
no- white have produced 26 young, 11 Red and 15 Red no-white. 
SUMMARY. 
Sections I and II. Amongst the stock of Gammarus chevreuxi which 
had been kept under Laboratory conditions for at least two years a 
small number of animals appeared in which the coloured retinal pigment 
was absent, whilst the white extra-retinal pigment remained. The 
experiments described in the present paper have shown that these eyes 
were of two different kinds. 
Eyes of the first kind were derived from a stock which originated in 
a cross between Black-eyed and Red-eyed animals, and were degenerate 
and irregular in shape. Four animals of this kind appeared in one 
brood, and such eyes have since been seen only in direct descendants 
from these. Hyes of this kind were found to behave as simple Mendelian 
recessives to eyes showing coloured retinal pigment, whether that pig- 
ment was red or black, and they are referred to in this paper as “ albino ” 
eyes. 
Eyes of the second kind were derived from a pure red-eyed stock, and 
were perfect in shape. The absence of coloured pigment has been shown 
not to be inherited, and the one animal of the kind experimented with, 
when mated with a female of the first kind, gave all coloured offspring. 
By a study of the descendants of these coloured offspring it has been 
shown that the parent animal behaves in inheritance exactly as if it 
were one with normal red eyes. 
In the course of this investigation all possible crosses have been made 
between Black-eyed, Red-eyed and Albino-eyed animals. In this way 
4 different kinds of black-eyed animals were produced, viz. pure black, 
black carrying albino, black carrying red, and black carrying red and 
albino; 2 different kinds of red-eyed animals, viz. pure red and red 
carrying albino ; 3 different kinds of albinos, viz. albino carrying black, 
albino carrying red, and albino carrying black and red. 
