THE PERCEPTION OF COLOUR 



629 



(1949) and Quaranta and Evans (1949) have shown that tortoises 

 [Clemmys, Testndo) can with perseverance be made responsive to 

 training techniques and therein show discrimination between blue, 

 green and orange ; as in fishes, red is apparently readily confused with 

 violet. So far as. lizards are concerned, Schlieper's (1927) experiments 

 with Lacerta vivipara using the optomotor reaction gave negative 

 results ; a positive response was elicited only by differences in bright- 

 ness. MusolfF (1955) had a similar experience with Angiiis and the 

 nocturnal ^.^-ko, Hemidadylus. Wagner (1932), on the other hand, 

 in training experiments using coloured papers associated as positive 

 stimuli with food or as negative stimuli with salt (which the lizard 

 violently dislikes), obtained evidence that colours were differentiated 

 from A\ hite or greys and that separate appreciation could be made of 

 red, yellow, green and blue ; this finding was corroborated in Anolis 

 for red, yellow-green and green but not for yellow and blue by Musolff 

 (1955) using the optomotor reaction as a criterion. It would appear, 

 therefore, that those Reptiles that have been investigated show the 

 potentiality of colour vision and that some lizards can base their 

 behaviour upon it. 



THE COLOUR VISIOX OF BIRDS 



That Birds possess a highly developed colour sense has always 

 been accepted partly because the bright colours of their plumage 

 obviously adopted as an attraction in mating would otherwise be 

 biologically inexplicable,^ and partly because of the proven ability of 

 some of them to pick out preferentially coloured flowers and fruit for 

 feeding. Recent experimental work has demonstrated beyond question 

 that this is indeed the case. 



The first scientific investigations were objective in nature. The 

 electroretinogram was utilized by Piper (1905) who showed that in 

 diurnal types such as the hen the maximal response occurred to wave- 

 lengths of 600 m^. in nocturnal types such as the owl, to 535 m/x ; he 

 concluded that neither type itself showed an individual Purkinje shift 

 but that this phenomenon could be demonstrated between the two 

 types. Shortly thereafter AbelsdorfiF (1907) and subsequently Laurens 

 (1923) and Erhard (1924) made a similar study on the differential 

 contraction of the pupil when the eye was illuminated by various 

 spectral bands and it was shown that a Purkinje phenomenon could be 

 elicited in a diurnal bird (the pigeon) provided an luiusually long time 

 (45 mins.) was allowed for dark-adaptation to develop. From an analysis 

 of their data these authors concluded that the mechanism necessary 

 for hue-discrimination existed and in general resembled that found in 

 man, but the illegitimacy of these conclusions we have already stressed. 



1 p. 104. 



Testudo 



Anijiiis 



Honidactylus 



