( xcix ) 



specimen of the Lihythea. It remains to be said that the 

 migration throughout was from S.S.W. to N.N.E., the wind 

 being light from the E.N.E. Five days after March 31st the 

 wind went round to the S.S.W. and blew strongly, the first 

 heavy rains falling two days afterwards. This observation 

 seems to indicate that butterflies which are usually non- 

 migi-ants may be stimulated by abnormal conditions to become 

 migrants, and that these occasional movements may enable 

 the species to occupy new ground." 



The special development of Mimicry in forest Butter- 

 flies. — Professor Poulton brought forward a suggestion 

 received from Mr. C. F. M. Swynnerton as to one of the 

 causes which may have operated in the special development of 

 mimicry in forest areas. The suggestion, which may be con- 

 sidered as a supplement to Mr. Swynnerton 's earlier state- 

 ment published in the Proceedings, 1912, pp. li-liii, was made 

 in a letter written by him on May 25th of the present year. 

 Mr. G. A, K. Marshall, who was familiar with the locality 

 (Chirinda, S.E. Rhodesia) from which Mr. Swynnerton wrote, 

 and to whom the paragraph had been submitted, regarded it 

 as quite plausible and also novel : — ■ 



" I believe you are right in your view that the forest struggle 

 for life 'is of a different kind.' Thinking it over after 

 sending you my suggestion as to the possible dependence of such 

 phenomena on the habitat of the model's food-plant, it struck 

 me that a very frequently repeated observation of mine had 

 perhaps a direct bearing on the point. It is that flying insects 

 are often exceedingly difficult to recognise in forest as against 

 veld. It is by no means easy at once to decide on the colora- 

 tion of an insect seen flying in a blaze of light against a deep 

 shadow or vice versd : also they so frequently disappear behind 

 foliage after having been in view for a few seconds only. 

 Under those circumstances a mei'e trick of flight, or the 

 smallest splash of colour in common, have often caused me to 

 take the insect for something that is otherwise utterly unlike 

 it, and such a hesitation would usually cost a bird the insect. 

 In this way incipient mimics should stand a better chance in 

 forest than in open country and be more likely to survive 

 beyond the incipient stages. I had previously applied the 



