Explanation of fokm and coloueing. 223 



to this day, as will be apparent from some of the experiments to be described, 

 1 would not feel at all certain of being able to distinguish between these two 

 motives in every case. 



Number of Trials, etc. : It will be seen that the results of single trials in 

 these experiments have been sometimes by no means final, and that I nowhere 

 place the same reliance on them that I do on the mutually corroborative 

 results of several trials. It was in order to avoid so far as possible the sus- 

 picion that must necessarily attach to single tastings that the experiments 

 were, as already indicated, attempted on a fairly large scale. Again, in 

 numerous instances (indicated often by the word " persistently "), I have 

 offered and re-offered and rg-offered even an individual insect with the 

 greatest insistence in order to make sure that its refusal was thoroughly 

 genuine and well-considered. And throughout I have obtained that con- 

 sistency of result and that same general range of preferences from 

 Acrseinse, etc., upwards that I have referred to earlier. 



My method of offering, I ought to explain, was, unless otherwise stated, 

 to bring each insect up close to the bird's bill (or mammal's mouth), usually by 

 the forceps. This ensured a definite acceptance or refusal — there was no 

 possibility of the insect remaining unnoticed. It was, of course, imprac- 

 ticable in the case of the wild birds. 



" Inedibility " ; " [Jnpalatability." For reasons which will, I think, be 

 appreciated by anyone studying these experiments, I cannot help regarding 

 the use of the terms " edible " and " inedible " without qualification as some- 

 what highly misleading. It is true that a large Brachycerus is inedible to 

 a bulbul, and even to a roller, but it is not inedible to a bird, large enough 

 to swallow it, whose bill is capable of crushing it (e. g., Bucorax), or whose 

 digestive apparatus is capable of dealing with it uncrushed (e. g., Numida . 

 An Amauris or Acrcea is unacceptable at most times to insect-enemies 

 generally, but it is by no means " inedible." Given the appropriate degree of 

 gastric activity it may even be highly acceptable to any of them. The 

 difference between it and, say, a Precis cehrene is probably simply one of 

 frequency of attack, but that difference may be a highly important one. 

 Thus, even though it be itself very frequently attacked, a species that is only 

 acceptable when the crop is empty is likely (other things being equal) to 

 be considerably less frequently attacked than one that is acceptable at all 

 stages ; and even this advantage is sufficiently obvious to render it intelligible 

 that it may be of benefit to the latter insect to be sometimes mistaken for the 

 former. For how great the benefit might be, see (for example) experiment 

 29, in which no less than 40 butterflies, including 14 large Charaxes, were 

 eaten by Roller B after she had tried and rejected a Mylotliris agatliina^ 

 and 37 butterflies, including 12 large Charaxes, after her similar 

 rejection of a Terias. I could multiply instances as striking or possibly 

 better, and there is nothing I think that more vividly brings home to 



