DIFFERENTIATION, MIGRATION, AND MIMICRY. 379 



became established on the one side, and sedentary habits on 

 the other. 



If there be one question on which the field-naturalist may 

 contribute, as lion's provider to the philosopher, more than 

 another, it is on the now much disputed topic of " mimicry," 

 whether protective or aggressive. As Mr. Beddard has remarked 

 on this subject, " The field of hypothesis has no limits, and what 

 we need is more study" — and, may we not add, more accurate 

 observation of facts. The theory of protective mimicry was first 

 propounded by Mr. H. W. Bates, from his observations on the 

 Amazon. He found that the group of butterflies, Heliconiidce, 

 conspicuously banded with yellow and black, were provided with 

 certain glands which secrete a nauseating fluid, supposed to 

 render them unpalatable to birds. In the same districts he 

 found also similarly coloured butterflies, belonging to the family 

 Pieiidce, which so closely resembled the others in shape and 

 markings as to be easily mistaken for them, but which, unprovided 

 with such secreting glands, were unprotected from the attacks of 

 birds. This resemblance, he thought, was brought about by 

 natural selection for the protection of the edible butterflies, 

 through the birds mistaking them for the inedible kinds. Other 

 cases of mimicry among a great variety of insects have since been 

 pointed out, and the theory of protective mimicry has gained many 

 adherents. Among birds, many instances have been adduced. 

 Mr. Wallace has described the extraordinary similarity between 

 birds of very different families, Oriolns houruensis and Philemon mo- 

 lucccensis, both peculiar to the island of Bouru. Mr. H. 0. Forbes 

 has discovered a similar brown Oriole, Oriolus decipiens, as closely 

 imitating the appearance of the Philemon timorlauensis of Timor - 

 laut. A similar instance occurs in Ceram. But Mr. Wallace ob- 

 serves that, while usually the mimicking species is less numerous 

 than the mimicked, the contrary appears to be the case in Bouru, 

 and it is difficult to see what advantage has been gained by the 

 mimicry. Now, all the species of Philemon are remarkably sombre- 

 coloured birds, and the mimicry cannot be on their side. But 

 there are other brown Orioles, very closely resembling those 

 named, in other Moluccan islands, and yet having no resemblance 

 to the Philemon of the same island, as may be seen in the case of 

 the Oriolus phceochromus and Philemon gilolensis from Gilolo. 

 Yet the Oriole has adopted the same livery which elsewhere is a 



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