630 F. W. GAMBLE AND F. W. KEEBLE. 



another of a different tint ? Does prolonged darkness pre- 

 vent their recovery ? To some of these queries we are in a 

 position to give fairly confident answei'S. The long records 

 of Flasks A and B (p. 658) furnish evidence on the first and 

 last of these questions. 



Unfortunately, recovery can only be studied in specimens 

 in captivity, since it is impossible to mark down prawns 

 at large and find them again in the morning; but, speak- 

 ing generally, dark-coloured and boldly marked varieties 

 (lined and barred colour-forms) recover precisely to their 

 former tints ; and in cases where the colour is not the same 

 as that of the previous day the change is curiously enough 

 often in the direction of the tint of new weed placed with 

 the nocturnes the night before, even if the recovery takes 

 place in vessels completely screened from light. 



Eeturning to the change of colour in the dark we will 

 quote a case in detail (Flasks A and B, July 22nd to August 

 4th, 1898, pp. 664 — 667). We may consider specimen d, 

 which exhibits changes from brown through green to red. 

 One of two small brown Hippolyte varians was placed at 

 5 p.m., July 29th, in the flask with much Delesseria san- 

 guinea (which was, however, greenish red and not full claret- 

 coloured). The flask was exposed to diffuse light. On 

 the morning of the 31st, up to which time the prawn had 

 exhibited no colour-change during the day, it was " semi- 

 transparent, brownish.^' The flask was covered with black 

 cloth in the evening of the 31st. At 10.80 the next morn- 

 ing (August 1st) the prawn was lig-ht brownish green. 

 The Delesseria sanguinea was now replaced by finely 

 branched red and brown weed, the prawn appearing to 

 choose the red. The flask was covered on the evening of 

 the 1st, and at 7.20 a.m. (2nd) Hippolyte was pale brown 

 with a reddish tinge. At 10.5 a.m. this tinge was scarcely 

 perceptible. The change toward redness, be it noted, took 

 place in the dark, and so cannot be considered as being due 

 to a sympathetic colour reaction. The cover replaced at 

 10.5 a.m. (2ud) was removed at 2.5 p.m., and the colour of 



