366 Eye-Colour in Gammarus 



Matings in which one parent is a normal-eyed Coloured spotted 

 dorsally and the other a Coloured No-white give a much lower percentage 

 of spotted. For instance the coloured No-white male just quoted was 

 mated with an F^^ normal-eyed Red from the first female's offspring. 

 The number of young was 46 normal-eyed (39 unspotted and 7 spotted) 

 and 47 No- whites, i.e. a percentage of 15 spotted amongst the normals. 



Another mating of the same kind gave 77 unspotted Black and 

 10 spotted, 77 unspotted Red and 1 spotted; a percentage of 6'7 

 spotted. 



(6). Animals which become No-ivhite as they grow older. The 

 matings of these animals are remarkable for the fact that considerably 

 more than half the young hatched are spotted (140 unspotted to 180 

 spotted and 1 one-sided No-white), with the spots usually large and 

 several of them with more than the normal quantity of white pigment 

 in the eyes. If two such animals are mated together when young, 

 i.e. when some white pigment is present in the eyes, all the offspring 

 are normal. We have not yet had ready to mate at the same time 

 a male and a female in which all the white pigment had disappeared 

 owing to age, so that we can make no statement from actual observation 

 as to whether or not the offspring of such a pair would have white 

 pigment. 



The details of all the experiments are preserved at Plymouth. Our 

 best thanks are due to Miss A. R. Clark for valuable help in the care of 

 the broods and in the examination of the young for eye-colour and the 

 presence of spotting. 



EXPLANATION OF PLATE XIV. 



GaJmmarvs chevreuxi. All figures x 58. 



Fig. 1. Normal Black Eye (B) $. Age 4| months. Figured a few hours before 

 moulting. 



Fig. 2. Red eye darkened with age. $ I. E. (see p. 348). The drawing was made 18 

 months after the animal was hatched and after she had extruded her 24th brood. Up 

 to about a month of that time the eyes had been bright red. She laid four batches of 

 eggs after the drawing was made and was then eaten by a second mate. 



Fig. 3. Normal Albino Eye (A + B + i?) ? . Age 5^ months. 



Fig. 4. Red, No-white Eye (RN +^). Young ^. 



Fig. 5. Colourless (Albino, No-white) Eye. (AN-i-JJ)$. Age 94 months. 



Fig. 6. Head of Red-eyed male from Pure Red Stock. (R) showing (a) dorsal patch, 

 (b) small lateral spot position 1, and {c) anterior end of the stomach. 



Fig. 7. " Composite " coloured eye, referred to on p. 354. The eye was figured about 

 4 months before the animal, which was very old, died. 



CAMBBIDOB : PRINTED BY J. B. PEACB, M.A., AT THE UNIVERSITY PBES8. 



K 



