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362 by many enthusiastic students in bionomics. Solitary instances, or that of a single species without reference to its congeneric allies, afford but a doubtful testimony to mimetic resemblances. This was clearly seen and enunciated by Darwin himself:—"If Green Woodpeckers alone had existed, and we did not know that there were many black and pied kinds, I dare say that we should have thought that the green colour was a beautiful adaptation to conceal this tree-frequenting bird from its enemies; and consequently that it was a character of importance, and had been acquired through natural selection; as it is, the colour is probably in chief part due to sexual selection." In fact, much evolutionary controversy is simply intellectual fencing, and what Schopenhauer has defined as "controversial Dialectic, Dialectica eristica." Mimicry, again, is often much obscured by plates in illustrated books which are intended to support the theory. As an example, in the excellent 'Royal Natural History' appears a coloured plate, entitled "Mimicry in Insects." Here a number of various insects of different orders and diverse habits are brought together in the midst of inappropriate—or inartistic—foliage, with the result that there is no apparent or sufficient mimicry to deceive the most careless enemy, or the most inexperienced entomologist. In fact, as a support to the theory, one can only conclude that either nature, or the artist, is at fault. Again, a comparative immunity from attack is often ultimately proved to be alone the case. A recent writer has observed:—"It is well known, and I have myself observed, that all our 'Cabbage' Butterflies are immune from attacks of birds, presumably because of some unpleasant taste or smell. Wasps, however, have twice been observed by me in the act of devouring these butterflies. Earwigs, too, which undoubtedly possess an unpleasant smell when irritated, fall victims to Wasps, in spite of their malodorous attributes."

To conclude a discursus, which in itself appears somewhat controversial, it may be better to give some instances of