264 Mr. C. F. M. Svvyimerton on the 



XII. — On the Coloration of the Mouths and Eggs of Birds. — 

 I. The Mouths of Birds. By C. F. M. Swynnerton, 

 F.L.S., F.E.S., C.M.B.O.U. 



(Plate VII.^ and text-figure 6.) 



1. Introductory. 



When I was in England in 1908, my old friend Mr. G. A. 

 K. Marshall, regarding the accepted views on mimicry in 

 insects as in some ways unsatisfactory, urged me to carry 

 out, on my return to Africa, a long and critical series of 

 experiments and special observations to test the validity of 

 those views, as also of the various objections that had from 

 time to time been levelled against them : to try to find out, 

 in short, what really does occur in nature. 



In the course of this investigation, which continued 

 through several years, but was at first mainly concerned 

 with insects and the food of insectivorous birds, one very 

 interesting fact in particular came to light. It was un- 

 expected, and at first even unwelcome, for it clashed with 

 my preconceived view that most prey was " palatable.'^ 

 I will describe it below. Once accepted — and my animals 

 forced it on me — it suggested a good contributory explanation 

 for distinctive coloration, and, by doing so, induced me, 

 amongst other things, to experiment in the preferences of 

 bird- and egg-eating animals. 



I have given in detail a large number of my experiments, 

 including nearly all those on carnivorous animals, in a 

 paper read before the Liunean Society on the 15th of April, 

 1915. I there discussed the question of the reliability of 

 such experimentation as I shall describe in this paper, 

 touching on every objection which, to my knowledge, had 

 been brought against it, and stating the measures adopted to 

 render the experiments as reliable as possible. I also made 

 a preliminary statement of the bearing of my results 

 * For explanation of the Plate, see p. 293. 



