122 THE VALUE OF COLOUR 



chell recognized the wide difference in affinity, 

 shown by the distance between the respective 

 numbers ; for his catalogue is arranged to repre- 

 sent relationships. He observed, what students 

 of Mimicry are only just beginning to record 

 precisely and systematically, the coincidence 

 between model and mimic in time and space and 

 in habits. We are justified in concluding that he 

 observed the close superficial likeness, although 

 he does not in this case expressly allude to it. 

 One of the most interesting among the early 

 observations of superficial resemblance between 

 forms remote in the scale of classification was 

 made by Darwin himself, as described in the 

 following passage from his letter to Henslow, 

 written from Monte Video, Aug. 15, 1832: 



' Amongst the lower animals nothing has so much 

 interested me as finding two species of elegantly coloured true 

 Planaria inhabiting the dewy forest ! The false relation they 

 bear to snails is the most extraordinary thing of the kind 

 I have ever seen.' * 



Many years later, in 1867, he wrote to Fritz 

 Miiller suggesting that the resemblance of a 

 soberly coloured British Planarian to a slug 

 might be due to Mimicry. 2 



The most interesting copy of Bates's classical 

 memoir on Mimicry, 3 read before the Linnean 

 Society in 1861, is that given by him to the man 

 who has done most to support and extend the 



1 More Letters, i. 9. 2 Life and Letters, iii. 71. 



8 'Contributions to an Insect Fauna of the Amazon Valley.' 

 Trans. Linn. Soc., xxiii. 1862, 495. 



