260 MR. E. B. POTJLTON ON THE PROTECTIVE [Mar. 1, 



most complete opposite of that in which the larvae render themselves 

 conspicuous in various ways. The experimental evidence shows, how- 

 ever, that the larva has a most disag^reeahle taste and (almost certainly) 

 smell, so that the most ravenous of all my Lizards would not eat it. 

 It is perfectly clear that these two methods of protection are anta- 

 gonistic if present in the degree and kind possessed by this larva. 

 One of them must be useless and merely incidental, and as it is quite 

 certain that the highly specialized protective colouring and habits 

 of concealment are of value to the organism, the unpleasant taste 

 must be the useless character. And this was seen in its treatment 

 by the Lizard, for the larva was recognized at once as something 

 which was expected to be palatable, and was at first seized with great 

 vigour, and it was only when the larva was injured beyond hope of 

 recovery that its enemy recognized the unpleasant attributes and 

 relinquished it. I witnessed the whole process ; it afforded the most 

 instructive comparison with the reluctant and hesitating way in 

 which a very hungry Lizard would approach a highly coloured larva 

 which it knew to be distasteful. It was quite obvious that the 

 Lizard fully expected a palatable insect, and was greatly surprised at 

 the unwelcome result. After the larva had bled freely, another 

 Lizard approached, but did not taste the insect, evidently re- 

 pelled by the unpleasant smell of the freshly escaped fluids. It 

 is obvious that a larva of this kind, being unpalatable, and yet giving 

 off no strong smell from its surface, by which to warn its enemies, 

 belonging, moreover, to an immense group of similarly protected 

 insects of which the vast majority are highly relished, — it is certain 

 that such a larva can gain nothing by an unpleasant taste which can 

 only be appreciated after fatal injury, and which is not associated 

 with any colour, marking, or habit by which the disagreeable 

 experience could be remembered. 



We are therefore driven to the conclusion that the unpleasant 

 quality is in this case a merely useless character, probably some 

 incidental result of the physiological processes of digestion or 

 metabolism. But such a condition is most important on theoretical 

 grounds, for it at once supplies the necessary steps by which a species 

 can change from one protective method to another. The most 

 constant objection or difficulty which is raised against the explanation 

 of the rise of any well-marked structure or function as due to the 

 action of natural selection, deals especially with the initial stages. 

 It is asked how natural selection can accumulate the earliest variations, 

 which are (the objectors assume) of insufficient importance to act as 

 criteria by which life and death can be settled. Darwin set the great 

 example of giving a satisfactory answer to such objections by carefully 

 working out one by one those cases in which especial difficulty was 

 assumed. And here, by the instance of the larva of M. typica, we 

 see at once how the difficulty of the origin of nauseous forms may 

 be overcome; for this larva possesses a useless attribute ready-made 

 as the incidental result of some physiological process, and at so high 

 a stage of efficiency that there is no difficulty whatever in imagining 

 that it might readily oecome an important criterion of existence. 



