Published online by Cambridge University Press: 11 May 2009
1. Twenty-one thousand, five hundred and fourteen (21,514) amphipods of the species Gammarus chevreuxi Sexton have been examined for eyecolour, 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.
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.
* Pair I produced no young, the female throwing off the eggs; the male was then paired with three other females, two Black from the dredging, and one Red from the old stock; all laid eggs, but no young were hatched, and the male died.
* Only one specimen has been recorded from freshly captured animals, a male, with the left eye affected.