654 suiniARY OF current researches relating to 



Sense of Colour among some of the Lower Animals.* — Some 

 years ago M. Paul Bert made a series of interesting experiments •with 

 the common Daphnia, exposing them to light of ditt'erent coloui's, and 

 he 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 t Sir John Lubbock has shown that on 

 the contrary 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 Mereschkowski who maintains that though the Daphnias 

 prefer the yellow rays which are the brightest of the spectrum they 

 are in fact attracted not by the colour but by the brightness ; that, 

 while conscious of the intensity of the light, they have 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 rather 

 than for any particular colour. To test this, however, Sir John 

 Lubbock took porcelain troughs about 1 in. deep, 7^ in. long, and 

 2.^ in. broad. In these he put fifty Daphnias, 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 of the Daphnias 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, one-half of the second with a green solution, one-lialf of the 

 thii'd wdth an opaque plate, and he threw over one 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 of the Daphnias 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 is evident, then, that in the first and second 

 troughs the Daphnias did not go under the solution for the sake of the 

 shade, because others placed by their side 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. Xo such result was given with blue 

 or red solutions. In such cases the Daphnias 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 coui'se possible that rays 

 of different wave-lengths produce different impressions upon their 



* Journ. Linn. Soc. (Zool.) xvii. (1883) pp. 205-14. 

 t Ibid., xvi. (1882) p. 121. 



