556 Mr. C. F. M. Swynnerton on 



a good differentiating character : my view that distinctive- 

 ness in nests generally is quite largely for recognition by 

 enemies, is at first sight in contradiction with the suggestion 

 of mimicry between eggs in unlike nests. I showed at the 

 B. O. C. meeting that these objections are not insuperable. 

 Either synaposematism or the view that the nest-appearance 

 is only a first line of defence, and the egg-coloration a last 

 resort, will meet the third of them ; while it is not necessary 

 to suppose that polymorphism even here is purely or in its 

 origin a matter of mimicry, or that the mimicry when it 

 arose was necessarily at first perfect. 



8. Darkness of certain nests, which nevertheless contain 

 coloured eggs, is an objection to any view that regards the 

 coloration of eggs as a visual appeal. I judge from my own 

 special observations, liowever, that the darkness is seldom 

 absolute ; and it must be remembered that an enemy, 

 unable to digest certain eggs or disliking their taste, and 

 relying on sight for their recognition, may even try not to 

 block out all light. So far as nestlings' mouths are con- 

 cerned, these are usually at once directed, on craning neck, 

 towards or through the opening. This is true even of birds 

 that have the opening in their nests below. 



9. Recognition by scent an objection. — I have constantly 

 known mammals (including my eaters of eggs) that rely 

 very much on scent for recognition, satisfied with mere 

 appearance, and deterred thereby from smelling. It would 

 even seem to be the rule, once the appearance has been well 

 learnt and while it is well remembered, and the smelling of 

 such eggs that occurred in my experiments was often the 

 result of pressure on my part. 1 have even known such 

 animals mistrust the evidence of their noses when it 

 seemed to conflict with that of their eyes, though this is 

 probably quite unusual. There can be no doubt that they 

 must be regarded as a serious factor in the matter of colo- 

 ration^ even when we have excluded all that are exclusively 

 nocturnal, and allowed for the fact that the olfactory appeal 

 will often succeed where the visual appeal has failed. At 

 the same time I regard it as one of the stronger objections 



