INHERITANCE OF EYE-COLOUR IN GAMMARUS. 23 
hd 
The following scheme shows the origin of this red-eyed stock, clear 
circles indicating the red-eyed, black circles the black-eyed animals :— 
Ba aA PAIR /. 
iS @ % OY Freshly eS r 5@® 
1+ brood ' ee) Ba age 
9g ew see 74.8 
227 brood. 
i Os 
4° brood 40 38@ 
(died) hls 
cre ee 36.@ teosicn 
(died) 
f 4QO 16.@ 
Recessive Stock Hybrid Stock p. 22 
P- 6 
8.0 49.@ 
* The male of Pair A mated with two of the other females of the same brood ; the 
resulting young numbered 27, all black-eyed. 
It cannot, of course, be stated as an absolute fact that red-eyed speci- 
mens never occur in the ditches in natural conditions, but so far not a 
single one has been found, although thousands of specimens brought in 
at different seasons of the year have been examined. The red strain has 
only shown itself in the one female, female A and her progeny. It seemed 
possible at first that the red-eyed strain could be accounted for on Men- 
delian lines. If the original Pair I had been a Pure Black mated with a 
Hybrid Black all the offspring would have been black-eyed, half the 
number Pure Blacks and half Hybrid Blacks ; and if in their matings a 
Hybrid should mate with a Hybrid the red-eye strain should have 
appeared. But, as far as can be seen, only the female A had the red 
strain; both her mates, male A and male S, when mated with other 
females (some from the same brood as female A and some from other 
stocks) had only black-eyed offspring, and, moreover, in none of the 
other members of the brood nor in their offspring has the red strain 
appeared. It might have been that male A was a Hybrid Black and that 
female A was the only Hybrid Black female in the brood, but it seems 
pushing coincidence too far to suggest that male S captured some months 
later and taken at random from a large dredging should be a Hybrid and 
