48 E. W. SEXTON AND M. B. WING. 
71(P.2& R. 3, and H. 2x R. 3) had 43 and 23, and 41 and 41 respectively, 
all except Exp. 70 being Hybrid Black and Recessive matings. 
Different rate of development.—There is often a marked difference in 
the rate of development of individuals in the same brood, and also of 
broods from the same pair. For example, in Exp. 85 (p. 38) some members 
of a brood hatched on January 6, 1915, were mature in March, the others 
not till June. Many instances like this were noted. 
In Exp. 99, Brood V took four months to reach maturity ; Brood VI, 
seven months; while Brood VII was mature in two months, and the 
animals were then much larger than many of the broods hatched three 
months earlier. 
It was found that Bacteria greatly retarded growth; in one case a 
female took eight months to become mature, and was then only about 
half the normal size. 
SUMMARY. 
1. Twenty-one thousand, five hundred and fourteen (21,514) amphipods 
of the species Gammarus chevreuxi Sexton have been examined for eye- 
colour, 21,302 referred to in this paper, and 212 in other experiments, 
not included. 
2. The normal eye-colour of this species is black, with a superficial 
reticulation of opaque white pigment. 
3. The pigmentation of the eye is very variable within limits. Eyes 
have been observed either partially or entirely lacking in the coloured 
pigment of the retinular cells, or with either a partial or entire lack, or 
else an excess of the opaque white pigment. 
6 
4. The red strain appears to have arisen as a “ sport” in the second 
generation of offspring of the first animals captured. No red-eyed animals 
have yet been found in natural conditions, although many thousands have 
been brought in from time to time and examined. Those counted for the 
purpose while the work for this paper was in progress numbered 8697, but 
this figure does not include the many thousands previously observed. 
Experiments have been made repeatedly with a view of getting the Red 
strain again from the Pure Black, but with no success. 
5. The Red eye-colour is not a sex-limited character ; about as many 
males as females come to maturity. 4248 red-eyed animals have been 
examined, 4175 referred to in the paper, and 73 in control experiments. 
6. The inheritance of the coloured pigment of the eye follows the 
Mendelian law— Black is dominant and Red recessive. The dominants 
are divided into Pure Black and Impure or Hybrid Black. 
