HTPPOLYTE VAEIANS. 637 



vessels were nocturnal, thougli the depth of the nocturnal tint 

 vai'ied. Those in the former were all nocturnes of differino* 

 degrees, the latter were fully nocturnal. The next day, 

 September 4th, 12.30, soon after noon all the specimens had 

 recovered ; those in the covered flasks had completely regained 

 their diurnal tint, and even the amputated specimens had ac- 

 complished the change as fully as the rest. This had come about 

 while the interior of the covered flasks was absolutely dark. 

 In the evening (9.50, September 4th) the amputated speci- 

 mens were clearly behind the others in assuming the nocturnal 

 phase; indeed, the two specimens in Flask D as yet showed 

 no signs of its appearance, while the remainder were full 

 "nocturnes." On the next morning (September 5th) the 

 amputated prawns were brown or reddish brown, the normal 

 ones in the covered Flask A were transparent green, and the 

 control specimens in had assumed the tints they started 

 with on September 3rd. In the afternoon the only change 

 was an increase of transparency in Flasks D (covered), 

 C (control), and a slight greening effect in the latter, so tliat 

 the normal prawns in A had not fully recovered their diurnal 

 tints. At 7 o'clock (it being only dusk) C (control) was in 

 the transparent green stage; the remainder were all nocturnes, 

 some fuller than others. At this point the experiment was 

 directed from the effect of constant darkness to ascertain the 

 effect of short exposure to incandescent light. The most note- 

 worthy point was that the T^ecovery of the amputated speci- 

 mens was as complete as those of the normal controls, but 

 that result is beside our present object. The experiment 

 shows that although the Flasks A, B, and D are kept in 

 constant darkness, yet there is the same succession of 

 diurnal and nocturnal colour-phases as is characteristic 

 of the prawns under natural conditions. It also shows that 

 darkness has some effect in retarding the normal times at 

 which these phases recur, and in weakening them. Further 

 evidence of the periodic colour-change is seen in Table X 

 (constant dark experiment, August 26th to 28th, 1898), and 



VOL. 43, PART 4. NEW SERIES, y Y 



