362 THE ZOOLOGIST. 



Bert made a series of interesting experiments with the common Daphnia, 

 or Water Flea, which is abundant in ditches and pools. He exposed them 

 to light of different colours, and thought himself justified in concluding 

 from his observations that their limits of vision, at both ends of the 

 spectrum, are the same as our own, being limited by the red at one end 

 and the violet at the other. In a previous communication Sir John 

 Lubbock showed, on the contrary, that they are not insensible to the 

 ultra-violet rays, and that at that end of the spectrum their eyes were 

 affected by light which we were unable to perceive. These experiments 

 have recently been repeated by M. Merezkowski, who, however, maintains 

 that though Daphnia prefers the yellow rays, which are the brightest of 

 the spectrum, it is, in fact, attracted, not by the colour, but by the 

 brightness; that, while conscious of the intensity of the light, it has no 

 power to distinguish colours. Given an animal which prefers the brightest 

 rays, it may seem difficult to distinguish between a mere preference for 

 light itself and a preference for any particular colour. To test this, how- 

 ever, Sir John Lubbock took porcelain troughs about an inch deep, eight 

 inches long, and three inches broad. In these he put fifty specimens of 

 Daphnia, and then, in a darkened chamber, threw upon them an electric 

 spectrum, arranged so that on each side of a given line the light was 

 equal, and he found that an immense majority preferred the green to the 

 red end of the spectrum. Again, to select one out of many experiments, 

 he took four troughs and covered one-half of the first with a yellow 

 solution, half of the second with a green solution, half of the third with an 

 opaque plate, and he threw over half of the fourth a certain amount of 

 extra light by means of a mirror. He then found that in the first trough 

 a large majority preferred being under the yellow liquid rather than in the 

 exposed half; that in the second a large majority preferred being under 

 the green liquid rather than in the exposed half; that in the third a large 

 majority preferred the exposed half to that which was shaded; and in the 

 fourth that a large majority preferred the half on which the extra amount 

 of light was thrown. It was evident that in the first and second 

 troughs they did not go under the solution for the sake of the shade, 

 because others placed beside them, under similar conditions, preferred 

 a somewhat brighter light. It seems clear, therefore, that they were able 

 to distinguish the yellow and green light, and that they preferred it to 

 white light. No such result was given with blue or red solutions. In such 

 cases they always preferred the uncovered half of the trough. It is, of 

 course, impossible absolutely to prove that they perceive colours, but these 

 experiments certainly show that rays of various wave-lengths produce 

 distinct impressions on their eyes; that they prefer rays of light of such 

 wave-lengths as produce upon our eyes the impression of green and yellow. 

 It is, of course, possible that rays of different wave-lengths produce different 



