232 DARWIN'S LETTERS TO R. TRIMEN 



It examined the mark and more than once at- 

 tempted to seize it. This observation has been 

 repeated with birds and African butterflies by 

 Mr. Guy Marshall and others, while large numbers 

 of specimens have been collected with injuries 

 to the wing at or near an eye-spot. Hence the 

 conclusion that the usual value of these mark- 

 ings is to divert attention from the vital parts 

 and give the insect extra chance of escape. Their 

 disappearance from the dry season broods is in- 

 terpreted as due to the paramount necessity for 

 concealment during that time of special stress.' 



9. 



Jan. 2nd [1868] Down. 



Bbomlet. 



Kent. S.E. 

 My dear Mr Tbimen 



What you say about the ocelli [ocellated spots or 

 eye-rspots] is exactly what I want, viz the greatest range 

 of variation within the limits oi' the same species, — 

 greater than in the Meadow Brown, if that be possible. 

 The range of difference within the same genus is of 

 secondary interest; nevertheless if you find any good 

 case of variation, I sh* much like to hear how far the 

 species of the same genus differ in the ocelli. As I know 

 from your Orchid Drawings how skilful an artist you 

 are, perhaps it would not give you much more trouble 

 to sketch any variable ocelli than to describe them. — 

 I am very much obliged to you for so kindly assisting 



' For a further account of this and other uses of these markings, 

 together with references to the original memoirs, see ' eye-spots ' 

 in index of Essays on Evolution (1908), 424. 



