618 F. W. GAMBLE AND F. W. KEEBLE. 



in the afternoon and early evenings of August^ 1898^ and 

 always with the same general result. The change in B 

 (muslined jar) and in C (porcelain jar), no matter what forms 

 are contained therein, is in the direction of green or blue. 

 All transitions towards these colours are found, including 

 some so completely modified as to appear of a bright trans- 

 parent azure blue. Speaking chromatophorically, the effect 

 of a short sojourn of the prawns in these jars is a general 

 retraction of the red pigment, and a slight expansion of the 

 blue accompanied by increase in transparency. Brown 

 specimens become green; "black-barred/' greenish-barred; 

 "red-liners," green-lined; and pink, mauve. If these speci- 

 mens are kept in muslined flasks, or in white jars with muslin 

 covers, under a good circulation, and supplied with food in 

 the shape of small pieces of weed or dead Crustacea, the 

 diurnal coloration remains green or bluish according as the 

 specimens contain much or little yellow pigment. Whereas 

 if, under the same conditions, a quantity of weed of one or 

 more colours is introduced, the red pigment is extruded ; 

 bluish-lined and barred prawns becoming black-lined and 

 black-barred, and some green ones turning brown. 



The greening effect is also well shown by a short exposure 

 of Hippolyte varians of different tints in a white porce- 

 lain dish either to diffuse light, or — in which case the result is 

 more marked — to sunlight or incandescent light. The change 

 is very rapid, a few minutes' exposure being sufficient to induce 

 the green or blue effect. Some of the evidence for this is given 

 on Table VI (Light Intensity, Expt. 2), where the chromato- 

 phoric changes are also recorded. Five brown prawns were 

 chosen. They were placed, one (E) in a black jar ; another 

 (F) exposed to sunlight in a glass dish on a black plate ; a 

 third (I) in glass jar half filled with dark grey sand; and the 

 two remaining prawns (G and H) in a white porcelain dish. 

 The experiment was begun in the garden at 12.30, in cloudy 

 weather with occasional gleams of sun. At 2.30 G and H 

 had lost most of their brown colour and had become greenish, 

 G particularly ; I was altered to a darker brown ; F was 



