632 F. W. GAMBLE AND F. W. KEEBLE. 



tlie other to tlie retention of the nocturnal phase. Gi-een, in 

 fact, is, in this case, incomplete recovery. Red, on the other 

 hand, is a colour specially induced during the diurnal phase 

 by light of low intensity, and at the onset of the nocturnal 

 phase; while dark brown is nothing more than the extreme 

 expansion of red, in a prawn well provided with yellow and 

 blue. A change in the dark, therefore, from green to brown 

 or from pale brown to reddish brown (such as we have just 

 shown) indicates, in the evening, the oncoming nocturnal 

 hue J • in the morning or afternoon the recovery therefrom 

 to the diurnally pigmented condition. Changes of colour, 

 then, occur, and some of these changes, though they occur in 

 the dark, are of a more or less " sympathetic " nature, i. e. 

 changes which tend to effect a match between the creature 

 and the weed. The experiments, however, seem incon- 

 clusive ; and not these only, but many others which we made 

 with a view to settling this curious point. 



We believe this inconclusiveness is not due to faulty 

 methods, for the experiment is of the simplest kind, but in 

 reality indicates the nature of the explanation. Colour- 

 changes occur in the dark, to and from the nocturnal hue. 

 Greenness is frequently the mean between the daily and 

 nightly extremes. Normally in the dark, then, it will be 

 possible to catch a brown prawn going over to, or passing 

 from, the nocturnal condition, either in a reddish phase, or in 

 a green phase, or as a transparent blue nocturne, or in a fully 

 recovered brown stage. Hence the fact that some brown 

 prawns kept in the dark with Zoster a appeared green is 

 capable of explanation. Change in the opposite sense may 

 also occur, a green prawn becoming brown in the dark, for 

 what we call a green prawn has no well-marked colour in- 

 dividuality ; it may have been and indeed often has been, 

 during exposure to light of low intensity, of a reddish-brown 

 colour. At the moment of examination, after dark exposure, 

 it may be found as a nocturne presenting a remarkable colour 

 contrast to the weed on which it hangs. ^ If the ebb of the 

 > PI. 33, figs. 10, 11. 



