DARWIN AND BERGSON ON EVOLUTION 



effect, and such an origin by " mutation " implies that all arose in 

 their present form and together. It is far more probable that this 

 protective device was developed gradually from some excretion 

 that had to be got rid of, and was utilised in the wall of the cocoon, 

 rendering it opaque, dense, or unpalatable, like the crystals of 

 arragonite that form a yellow powder in the cocoon of the " Lackey 

 moth," or of oxalate of lime that confer hardness and density on the 

 cocoon of the " Small Eggar moth." It has grown up and matured 

 in a long succession of individuals that have never been in contact 

 with the lives of enemies. The far larger number that in each 

 generation were met by their foes have contributed nothing to this 

 evolutionary history ; for they have left no descendants. What is 

 there in this past history to bring the instinctive " sympathy " or 

 " insight " into relation with possible enemies rather than with 

 species that do not attack the Deilemera ? In this and in all the 

 countless examples of the kind, the fact that the right enemies are 

 prepared for beforehand in the right way cannot be explained by 

 Bergson's hypothesis of instinct, nor by any other hypothesis as 

 yet propounded except the Natural Selection of Darwin and Wallace. 



Before passing to the consideration of my second subject — the 

 origin and growth of a mimetic resemblance — it is necessary to 

 attempt a brief discussion of Mimicry itself. 



Superficial resemblances of several kinds are to be found between 

 the forms of life inhabiting the same part of the earth's surface. 

 Thus a wonderful " protective resemblance " to plants is borne by 

 well-nigh innumerable insects, and many species of these, by their 

 likeness to the same vegetable form, such as lichen or bark, gain 

 incidentally a likeness to one another. That particular kind of 

 superficial resemblance known as Mimicry is not an incidental, but 

 a direct likeness borne by one animal, called the Mimic, to another 

 known as the Model. However close the likeness between two forms 

 may be, it is rarely difficult to decide between the Model, which pre- 

 serves its relationship with the patterns of allied species, and the 

 Mimic, which, in approaching the Model, has departed from the 

 appearance of its group. Indeed, in a high proportion, perhaps in 

 half of the mimetic species of butterflies, Mimicry is restricted to 

 the female, while the male bears the ancestral pattern of the group 

 to which the species belongs. 



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