INHERITANCE OF EYE-COLOUR IN GAMMARUS. 47 
Another brood, Exp. 5, Brood 4, kept under the same conditions as the 
one just mentioned and breeding during the same time had 132 young. 
In the following four months, March to July, 1915, 91 young were 
hatched. 
The next brood of the same experiment, Exp. 5, Brood 5, shows a 
curious variation. There were the same number of individuals as in the 
last, the same conditions, ete. After six months’ breeding only 2 young 
were hatched from all the eggs laid, but in the following three months, 
April to July, 1915, 90 young were hatched. 
For instances of fertility and infertility in individuals some of the F, 
animals may be taken. Sometimes an animal will mate several times with 
no results; the most striking case of this was the H. female of Exp. 39 
(p. 36). Mated with a Black male, eggs were laid on September 12, 1914, 
carried for six days and then thrown off; eggs again on September 25 
and again thrown off before hatching. The male was taken away, and 
another Black male put in: eggs laid on October 9 and thrown off; eggs 
again on October 23 and again thrown off. Then the female was left for a 
period without a male. On November 29 the male was put back, and eggs 
were laid, a large number, thrown off some days later; eggs laid on 
December 14, a large number, thrown off; eggs laid on January 3, 1915, 
all there on January 12, but on the 14th they were all thrown off except 
two, these were carried a day or two longer but not hatched. The male 
was taken away, and a Red male put in, which died on January 26 
without any mating taking place. Then two more Red males were added 
—-one disappeared on February 8. The female laid eggs, very few, these 
were thrown off on February 11. The male was again changed. On 
February 17 eggs were laid, and from these 4 young were hatched on 
March 8. Eggs were laid on March 10 and 12 young hatched on April 3. 
A fresh brood laid on April 3, hatched out on April 23, 19 young. The 
male disappeared and another was put in. Eggs laid on June 1, very few 
in number. On June 9 the male ate the female. The seven males used 
in this experiment, 2 Black and 5 Red, were all healthy animals, which 
had already fertilised the eggs of other females. 
Numbers in Broods.—As a rule it is found that an exceptionally large 
brood of young is followed by a very small brood, or by the omission of 
one period of sexual activity, but in several cases the animals had a series 
of large broods, the highest numbers recorded in two succeeding broods 
being: In Exp. 11 (R. 2 mated with H. 3), 42 in the brood and (mated 
directly after with another H. 3, Exp. 20) 44 in the next; in Exp. 51 
(H. 9 x R. 3), 40 and (mated then with H. 3, Exp. 106) 52, the largest 
number in a brood yet recorded; Exps. 60, 68, and 104 (H. 3 x R. &) 
had 47 and 31, 30 and 48, and 40 and 43 respectively, and Exps. 70 and 
