INHERITANCE OF EYE-COLOUR IN GAMMARUS. at 
in many cases observed, reached maturity before the black-eyed in the 
same brood. Yet, if left to breed together with no admixture of the black- 
eyed strain, they gradually diminish in numbers, throwing off the eggs 
sometimes soon after deposition, or dying after having had only one or 
two broods. Seven of the ten stocks have failed in this way. 
The results of the Experiments with the Parent Generation are given 
below in detail, and are typical of'all the experiments with inbreeding 
Recessives. They are as follows :— 
Exp. 1. Two broods, 10 and 12 respectively ; female died. 
, 2. Mated, but no eggs laid. 
,, 93. One brood ; only | young hatched. 
,, 4. One brood of 20 young. 
,, 9. First brood, only 1 young hatched ; second brood, 3 young. 
Thinking the small numbers might be due to some defect or 
unhealthiness in this male, it was taken away and another 
added. Third brood, only 1 young hatched, Male again 
changed. Fourth brood, 14 young; fifth brood, eggs thrown 
off before hatching. Male again changed. Sixth brood, 17 
young. 
,, 6. One brood, 19 young. A second brood was laid, but the female 
died before the eggs were hatched. 
,. 1. Mated, eggs laid, but thrown off before hatching, probably un- 
fertilised. 
,, 8. Mated, eggs thrown off as in Exp. 7. 
,, 9. One brood, 10 young. A second brood was laid, but the eggs 
were thrown off before hatching. 
, 10. Mated, eggs thrown off as in Exps. 7 and 8. 
,, 11. Mated, eggs thrown off as in Exps. 7 and 8. 
The total results for six months for the Parent Generation were: One 
pair mated, no eggs laid; seven broods not hatched; eleven broods 
hatched, the young numbering in all 108; average per brood 9:8. Only 
about half of these survived to maturity. 
In the next generation, the F,, a rather different system was 
followed. In some cases records of separate pairs were kept, in other 
cases the whole brood was left together in a finger-bowl, each female 
removed after oviposition, kept separate until the eggs were hatched, and 
then returned to the brood-bowl to mate again. 
The total results in the twelve months from July, 1914, to July, 1915, 
for the breeding of the F, generation are: 2 pairs mated with no results ; 
80 broods from the other pairs, 20 of these not hatched, 60 hatched, 
