210 HUXLEY AND NATURAL SELECTION 



Similar considerations encourage the hope that we may 

 understand another feature which has been long known 

 to be characteristic of wet season forms, especially in 

 the Satyrinae, the group which includes our well-known 

 'Meadow-brown', 'Heath,' and 'Ringlet' butterflies. 

 I refer to the development of eye-spots on the under side 

 of the wings in wet season broods and their disappearance 

 in those of the dry. An observation made in 1887 by 

 Professor Meldola and the present writer throws light 

 upon the problem. I had introduced a ' Small Heath 

 Butterfly' {Coenonympha pamphilus) into the cage of 

 a lizard. It was at once obvious that the reptile was 

 greatly interested in the large eye-spot on the under side 

 of the fore wing ; it examined the mark intently, and 

 several times attempted to bite it. 1 Mr. Marshall has 

 also observed that a South African kestrel pecked out 

 the eye-spots from the hind-wing of a ' Swallow-tail ' 

 butterfly before eating any other part. 2 Furthermore, 

 captured butterflies are especially liable to exhibit injuries 

 in the vicinity of such marks. Some of these tears or 

 snips out of the wing afford very strong indirect evidence 

 that they were made by an enemy. ' 6 It is probable, 

 therefore, that such eye-spots as those of the Satyrinae, 

 which are placed on parts of the wing surface remote 

 from the body, are adapted to divert the attention of an 

 enemy from the vital parts, thus giving the insect another 

 chance of escape. Such directive marks will render the 

 butterflies more conspicuous during the periods of com- 

 plete repose, and we can readily understand that they 

 would be a great danger, and why they should be withheld 

 in the dry season. The fact that these markings are of 

 value in a period of activity and a danger in complete 

 repose, is also rendered probable by movements of the 

 fore wing which have been observed in many Satyrines, 

 changes in the attitude such as to reveal the eye-spot 

 during a brief rest when the insect is alert, but to conceal 

 it when the rest becomes prolonged. 4 It is probable, 



1 Colours 0/ Animals, London, 1890, pp. 206, 207. 



" Trans. Ent. Soc, Lond., 1902, p. 341. 



8 I.e. pp. 3 6 6-75- " l-c. pp. 37 2 > 440- 



