EXPLAXATION OF FORM AND COLOURING. 203 



Experiments and Observations bearing on the Explanation o£ Form and 



Colourino-, 1908-1913. By (J. F. M. Swynnerton, F.L.S. ^-^^tTTf. 



/-^^ 

 [Read 15th April, 1915.] /'^ 



1. GENERAL INTRODUCTION. \ „ " "^ 



A. AVoRK to be described. 



When I was in England in 1908 my old friend Mr. Gr. A. K. Marshall, 

 who, since he first guided my ardour for Natural History into useful channels 

 in the Natal Coast Bush and at Salisbury in 1897, has never ceased to help 

 and encourage me in every possible way, strongly urged me to carry out on 

 my return to Chirinda a series of experiments designed to test the validity of 

 the current theories of mimicry. He suggested the following programme: — 



" 1. The testing of every available butterfly (and where possible its 

 larva and pupa) on every available bird, and a rough classification of the 

 insects into grades of palatability for every animal used. 



" 2. The testing by a special series of experiments o£ Mliller^s assump- 

 tion that the experimental destruction would be the same for every 

 type of warning coloration. 



" 3. A careful account of the habits and flight of all distasteful species 

 and their mimics. 



" 4. The releasing of damaged butterflies to wild birds. 



" 5. Tests whether birds are deceived by resemblances in their prey.'"" 



Professor Poulton, in a letter dated May 26th, 1909, wrote : — "I am most 

 anxious to know about the edibility of the forms that, in my opinion, probably 

 belong to a second category of distastefulness — long behind the Danaines 

 and Acrseas, but still, I believe, distasteful . . . any forms that have fairl}^ 

 conspicuous undersides.'^ 



A little later he and Mr. Marshall independently suggested to me that I 

 should make a special point of investigating the defences of the larger species 

 of Cliaraxes. 



I would like to say at once that not only am I indebted to these two friends 

 for the inspiration to much work that I have found most fascinating and 

 absorbing, but that both have continued to be lavish of help and encourage- 

 ment and most generous in their gifts to me of their own and other publications 

 on the subject. I can say without exaggeration that any value that work may 

 possess is primarily due to them. And they have gone to immense trouble 

 over the identification of my insects. Also, I have to leave for Africa before 

 this paper goes to press and Professor Poulton, with the utmost kindness, 



HNN, JOURN. — ZOOLOGY, VOL. XXXIII. 1§ 



