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Show 192 MR. E. B. POULTON ON THE PROTECTIVE [Mar. 1, so as to resemble their surroundings, would be eaten when detected, and this prediction also seemed to receive complete confirmation." Thinking over the whole line of argument and its apparently complete confirmation, 1 was led to anticipate that a somewhat different method of conducting the experiments would lead to a modification and extension of Wallace's classification of the uses of colour, in the direction of greater elasticity. At the same time it seemed better to withhold the suggestion until 1 had taken the opportunity of submitting it to the experimental test. I was travelling in Italy a few weeks after delivering the lectures, and took the opportunity of capturing many individuals of a few species of South-European Lizards, and of one species of Tree-Frog (Hyla arborea, var. meridionalis). I was thus able to carry out the suggested experiments, which on the whole yielded results which confirmed the conclusions I had arrived at ci priori, and also produced other results which I had not anticipated. Some of these results were shortly communicated to the Biological Section of the British Association at Birmingham (1886), and an abstract is printed in the volume containing the papers read at that meeting. The suggested extension of Wallace's line of aigument, which has now been put to the proof, is as follows:- The acquisition of an unpleasant taste or smell, together with a conspicuous appearance, is so simple a mode of protection, and yet ex hypothesi so absolutely complete, that it seems remarkable that more species have not availed themselves of this means of defence. What can be the principle which works in antagonism to such a mode of protection 1 For in Wallace's theory no suggestion of a true counterbalancing limit appeared-i. e. one which increased with the increasing application of this method of defence, until the latter received a check or, for the time being, was rendered of no avail, or was even turned into an absolute danger. And yet it seemed probable that such an antagonistic principle would appear as the natural outcome of the too complete suecess of a method of defence which depends on the acquisition of an unpleasant taste or smell together with a conspicuous appearance. If a very common insect, constituting the chief food of one or more Vertebrates, gained protection in this way, the latter animals might be forced to devour the disagreeable objects in order to avoid starvation. And the same result might be readily brought about if a scarce and hard-pressed form adopted the same line, and so became dominant, after ousting many species which were much eaten by Vertebrates. If once the Vertebrate enemies were driven to eat any such insect in spite of the unpleasant taste, they would almost certainly soon acquire a relish for what was previously disagreeable, and the insect would be in great danger of extermination, having in the meantime become conspicuous by gaining warning colours. If the reasoning be correct, it is clear that this mode of defence is not necessarily perfect, and that it depends for its apparently complete success upon the existence of relatively abundant palatable forms : in other words, its employment must be strictly limited. It has, indeed, always been recognized that an insect may be distasteful to one Vertebrate |