INHERITANCE OF EYE-COLOUR IN GAMMARUS. 29 
matings of the Dominants with other Dominants and with Recessives 
should show the following results :— 
(a) P.xP.: mating of Pure Black with Pure Black should give all 
black-eyed offspring, Pure Black, which should breed true through all 
succeeding generations. 
(b) P.xH.: matings of Pure Black with Hybrid Black should give all 
black-eyed offspring, half Pure Black and half Hybrid Black. 
(c) P.xR.: mating of Pure Black with Recessives should give all 
black-eyed offspring, Hybrid Black, which when bred together should 
show the red-eyed strain in the next generation. 
(d) H.x H.: matings of Hybrid Black with Hybrid Black should give 
three black-eyed offspring to one red-eyed, 1.e. in the proportion of one 
Pure Black and two Hybrid Black to one Recessive. 
(e) H.xR.: matings of Hybrid Black with Recessive should give off- 
spring half of which would be Hybrid Black and half Recessive. 
THE PurRE BLACKS. 
Only a short note is necessary under this heading. 
The Pure Black stock (p. 22) has been kept and interbred for over three 
years inalargejar. Observations have been made on it at different seasons 
of the year, all the animals being taken out and examined for eye-colour. 
Different pairs also have been kept separate from time to time and their 
progeny recorded to the third and fourth generations, but in all the cases 
not a single red-eyed one has been found. 
With other dredgings brought in at intervals since June, 1912, the same 
results have been obtained. The last dredgings examined were those 
described on p. 25. 
With regard to the 194 young from the P. x P. matings mentioned on 
p- 41, the record of the number of their offspring has not been kept, it 
having been thought sufficient to examine the eye-colour of all the animals 
in the different bowls from time to time to make sure that no red-eved 
one appears. 
In the P. x H. matings which have been tried, the young were all black- 
eyed. The difficulty with these has been in bringing a sufficient number 
of any one brood to maturity in order to test them for P. and H. characters. 
Only one case succeeded well enough to be recorded, the Brood 1 of 
Experiment 118 referred to on p. 41. Twenty-two young were hatched, 
and twenty-one reached maturity—seven males, thirteen females, and 
one abnormal one. Each of these was mated with a red-eyed mate except 
