SEA-FISHEKIES LABORATORY. 151 



method consisted in testing the effect of light of differing 

 intensities upon a given variety. To do this a number of 

 jars, some of clear glass, others enveloped with muslin, 

 others again with black cloth, were taken on board, and as 

 soon as the nets were hauled up, the Hippolyte were 

 recorded-, and specimens of each variety were placed 

 in each jar. The effects produced differed very markedly 

 according to the time of day at which the catch was made ; 

 the result of treating a haul in this way after dark or even 

 in waning light being very different from that obtained at 

 mid-day. 



We also directed our attention to the influence of 

 variously coloured weeds, with the object of testing 

 whether a brown Hippolyte would become green when 

 placed with green weeds, and red when surrounded with 

 red ones. For this purpose we had devised an apparatus 

 which was described shortly before the British Association 

 at Bristol. 



This instrument consists of a "pressure-bottle," hold- 

 ing a couple of gallons of sea-water, which is discharged at 

 a uniform rate through an escape-tube commencing with 

 a minute opening. The water is made to circulate 

 through a series of air-tight observation- dishes, in which 

 the Hippolyte are placed. The loss of water from the 

 pressure-bottle is made good by the entrance of air which 

 is first drawn through a second series of observation- 

 dishes, the water in which is changed once or twice a day 

 only. On the whole it was found that Hippolyte flourishes 

 best in the air-circulating dishes. 



The influence of monochromatic light was investigated 

 by the aid of Landolt's fluid " colour-filters." In order 

 that the light which reaches Hippolyte may be of fairly 

 high intensity and not merely equivalent to shade, we 

 employed a mirror to reflect sunlight or the light of an 



