HIPPOLYTE VAKIANS. 631 



the prawn seen to be unaltered. Once again the cover was 

 replaced till 4,30 p.m. (2nd)j when examination proved the 

 prav^n to be a nocturne of a delicate blue-green colour. 

 After ten minutes' exposure to diffuse light the nocturnal 

 colour gave place to a dull pinkish brown (tail reddish) . On 

 August Brd, 9.35 a.m.^ after having been covered from 4.40 

 p.m. of the previous day, the prawn was seen to be very 

 transparent, middle of body pale greyish red, tail brighter 

 red. Four minutes' exposure in a white dish sufficed to 

 diminish the redness ; exposure for oue hour considerably 

 reduced the transparency. No further change occurring, it 

 was put with fine plumose red weed (3.50 p.m., August 4th) 

 and exposed to diffuse light. At 10.30 p.m. it had passed 

 from " faint red transparent" to dull brown. On August 

 5tli it had become bright red, and on this day it fell a victim 

 to a larger prawn in the same flask, a fate which overtook 

 not a few of our experimental animals. 



Another case may be given from our experiments. At 

 1 p.m., August 14th, 1898, four green and four brown 

 Hippolyte were taken and placed with some Zostera in 

 a current of water. At 4.50 p.m. six were greenish and 

 two brownish. They were at once covered and placed with 

 finely divided red weed. At 9.30 p.m., during momentary 

 examination, two nocturnes were observed. The next morn- 

 ing at 10.50 a.m. all (except one very transparent greenish 

 specimen) were brown with reddish tinge, while three were 

 markedly reddish. Replaced in the dark at 10.50 p.m. all were 

 nocturnes. The next morning two were nocturnal, two greenish 

 brown, one light brown, and one yellow-brown. Green weed 

 was now put in. They nocturned again at night, and the fol- 

 lowing day four were transparent and green, the rest brown. 



With reference to the changes occurring during the course 

 of this experiment, the following remarks may be offered. 

 A prawn of a colour other than green which recovers to 

 green (in the dai-k), especially after being in captivity a day 

 or two, does so, not in reference to any weed, but because it 

 is being acted upon by two impulses, one to full recovery and 



