bo 
=I 
—~] 
LOSS OF EYE-PIGMENT IN GAMMARUS. 
3 Red-eyed, viz. :— 
1 with constitution CC RR 
- io Ce RR 
2 
4 Albinos, viz. :- 
1 with constitution ¢ ¢ BB 
Ts us ce RR 
ce BR 
For 119 specimens the numbers should be according to theory 
67 black, 22 red, 30 albino, 
whilst those found by experiment were 61 black, 28 red, 30 albino, 
a sufficiently close agreement. 
y) 
4 39 
FA. Generation. Red x Red. 
The six red-eyed young of the F, generation were 4 females and 
2 males (Plate I: I.D.E.F.G.H.J.). The males were mated with the 
females and 875 young were obtained, including a brood of 17 not ex- 
amined within 48 hours of extrusion.* 
According to theory the parents all had the constitution CeRR, and 
these mated together should give : — 
3 Red-eyed, viz. :— 
1 with constitution CC RR 
20s Ce RR 
1 Albino ss . eve RR 
Experiment gave 658 red-eyed and 217 albino,t theory requires 656 
red-eyed and 219 albino. 
FA. Generation. Black x Red. 
A cross between a red-eyed female and black-eyed male of the F, 
generation (PI. I: I.B. and D.) gave in three broods 9 black-eyed, 15 red- 
eyed and 8 albino. Theory requires the proportions 3 black, 3 red, 2 
albino, which for 32 young would be 12 black, 12 red, 8 albino. 
* Unless the young are examined and removed soon after they are extruded a certain 
number are lost through being eaten by the parents and the more delicate ones tend to 
disappear first. The albinos seem to be more delicate than the reds, and the reds than the 
blacks, so that unless the broods are counted within a short time the proportions of the 
different coloured eyes are liable to error. THE FIGURES GIVEN IN THE PRESENT PAPER 
INCLUDE ONLY SUCH BROODS AS WERE COUNTED WITHIN FORTY-EIGHT HOURS OF THE 
TIME OF EXTRUSION, UNLESS THE CONTRARY IS DEFINITELY STATED. 
+ Of these 589 red-eyed and 191 albinos came from the mating of one pair. (1.F. x LE. 
Plate I, see p. 336). 
