360 Eye-Colour in Gammarus 



These last two pairs were then crossmated, the results obtained were : 

 from the male of pair 1 mated with the female of pair 2 there were 81 

 unspotted offspring and 16 spotted, a percentage of 16"5. From the 

 other pair (male of (2) and female of (1)) there were 129 unspotted and 

 7 spotted young, a percentage of 5*1. 



An experiment from the family of the (6) group, which gave no spots 

 in the F^ generation, is interesting. Two F^ young Reds were mated and 

 had 180 young before the first spot appeared. In all, there were 275 

 unspotted and 6 spotted, i.e 21 °/„, but the other 5 spotted all came in 

 the last brood, the male dying before the eggs were hatched. 



The Spatted Pairs. For comparison with these unspotted pairs 

 a number of spotted pairs having the same origin were mated. Only 6 

 spotted adult animals could be found in the stock ; their spots were all 

 small and lateral. The percentage of spotted offspring was, on the 

 whole, less than in the matings of the unspotted. One family gave 176 

 unspotted and 7 spotted, a percentage of 3'8, and another gave 88 all 

 unspotted. 



It has been found impossible to get a Pure Unspotted Stock. 

 A mating of Unspotted x Unspotted gave 57 unspotted young in the 

 Fi generation, but the spots appeared in the next generation. 



Another mating, Spotted x Spotted, is remarkable from the fact 

 that the spotted animals gave 88 all unspotted young. The spots, 

 however, reappeared in the F^ generation, the principal types of spots 

 being represented, dorsal, lateral, and on the 1st peraeon-segment. 



The lowest percentage of Spotted in the F^ generation was obtained 

 from the 1*8 °/„, Experiment X. The Unspotted young were mated 

 together, but the spots appeared again in the percentage of 1*6 spotted. 

 Taking all the offspring of the Unspotted F^ matings in this experiment, 

 1617 were hatched, of which 27 were spotted. 



In the Experiment IX, which gave the highest percentage in the 

 F^ generation, 18°/„, the Unspotted F^ were mated together and 1863 

 young were produced, of which 71 were spotted, i.e a percentage of only 

 3'8 spotted. 



An attempt was made to mate the Spotted F2 young from the 

 different experiments, to find what proportion of spotted would be given. 

 Unfortunately many died, and only two or three large families could be 

 obtained, not enough to base conclusions on. 



It would seem, however, that animals with large dorsal spots give 

 the largest number of spotted young. One pair, both spotted dorsally. 



