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AFRICAN MIMETIC BUTTERFLIES 



suggestions as to the mutual relations of living creatures should always be received with 

 caution in the absence of precise data concerning the conditions under which they maintain 

 their position in the struggle for existence. 



Since the publication of Bates's original paper, many observations bearing on the 

 subject have from time to time been communicated to the various learned societies and 

 scientific journals. Wallace's paper in the Transactions of the Linnaean Society, 1866, 

 vol. XXV, supplied numerous striking instances of mimicry from the Eastern Tropics, and 

 Trimen dealt with the same phenomena in the Ethiopian region in his paper read before 

 the same society in 1868. It is to this latter naturalist that we owe the discovery of one of 

 the most curious and complicated instances of protective mimicry with which we are at 

 present acquainted, namely, that of the polymorphic mimetic forms of Papilio dardanus. 

 In 1882 Professor Raphael Meldola published a paper in the Annals and Magazine of Natural 

 History in which he supports the theory of Miillerian mimicry, and shows how it may be 

 made applicable even to the cases which have been observed of resemblance between butter- 

 flies of nearly related species. The question as to which is the model and which is the mimic 

 does not, under such circumstances, require to be decided, since under the hypotheses 

 already mentioned each species will benefit in a fixed proportion to the number of individuals. 



It may be here noted that the phenomenon of mimicry in relation to sex presents many 

 interesting peculiarities. In some cases the sexes of the mimic are similar and resemble one 

 model. In others both model and mimic may be sexually dimorphic, when the corresponding 

 sexes resemble each other. There are cases where the dimorphic sexes of a mimic resemble 

 models of different species, whilst a non-mimetic male may have more than one form of 

 female, each resembling a different model. It will be found, however, that in very many 

 cases the female only is mimetic, the phenomenon being thus frequently associated with 

 sexual dimorphism. This special development of mimicry in the female sex was originally 

 explained by Wallace (loc. cit.) on the supposition that ' their slower flight, when laden 

 with eggs, and their exposure to attack while in the act of depositing their eggs upon leaves, 

 render it especially advantageous for them to have some additional protection '. An 

 interesting discussion on this point will be found in Professor Poulton's essay on * The 

 Value of Colour in the Struggle for Life '} It is there pointed out that while Wallace's 

 hypothesis would in large measure account for the facts, it may be doubted whether it 

 offers a complete explanation, and that amongst other considerations the greater colour 

 variability of the female may have been an important factor in determining the predominance. 



Consideration of other features of the subject will be found in the latter part of this 

 volume. Batesian mimicry presents a comparatively simple aspect of the case, whilst 

 mimicry between distasteful forms may be, and frequently is, of a highly complicated 

 nature. As already pointed out, it is based on the inability of insectivorous foes to distinguish 

 instinctively between edible and distasteful species. It has been asserted that young 

 creatures do know what to touch and what to avoid, though such experiments as have been 

 made have given results which are in favour of the contrary view. It has been pointed 

 out that birds must know how to avoid poisonous berries, otherwise they would be destroyed 

 by eating them. It seems questionable, however, whether many berries are in fact poisonous 

 to birds. The formation of berries is a development which has been attained by plants for 

 the better dissemination of the seeds which the berries contain and the object of the berries 

 is to attract birds in order that the seeds may be eaten and distributed by the natural 



^ ' Darwin and Modern Science,' Essay XV, p. 292. Cambridge, 1909. (Reprinted in ' Darwin and The 

 Origin,' Poulton. London, 1909.) 



