INTRODUCTION 



23 



processes of digestion, which do not destroy the germinating principle of all the seeds ; and 

 even if the previous assertion were proved, it seems impossible to understand how any 

 animal can have inherited an instinctive knowledge of all the many and varied butterflies 

 which are unfit for food, and it should be borne in mind that whilst a butterfly, or even 

 a berry, maybe distasteful, it need not be actually poisonous. Also it should not be forgotten 

 that distastefulness is not an absolute property. There may be, and almost certainly are, 

 wide differences between species in the degree of their distastefulness. Such differences 

 might even account for Miillerian mimicry of a comparatively rare by a numerous species, 

 provided the former were considerably more objectionable than the latter. These considera- 

 tions, together with other interesting questions which arise, will be more conveniently 

 appreciated after a closer acquaintance has been made with some of the instances of 

 mimetic resemblance presently to be described. It will be seen that the subject of mimetic 

 association in Lepidoptera falls under two heads of the table of animal coloration given 

 above. Imitation of a distasteful species by a butterfly which is of an edible kind, the 

 phenomenon known as Batesian mimicry, is a form of pseudaposematic coloration. The 

 mimetic groups formed by the resemblance of two or more distasteful species (Miillerian 

 mimicry) form a special case of aposematism, and the forms are spoken of as synaposematic. 



Butterflies, then, form a large group of insects whose structure differs sufficiently to 

 enable us to divide them into various families and genera. Although they are all butterflies, 

 these differences from an anatomical point of view are great. Many butterflies, however, 

 between which such differences occur, by a special modification of colour and form, superficially 

 resemble each other so closely that they are only to be distinguished by a careful examination. 

 These resemblances have been attributed to distasteful properties possessed by certain species, 

 the appearance of the latter having come to be simulated either by other nauseous forms 

 or by species which are in reality edible, the process of selection by insectivorous enemies 

 having been the primary influence which, working on favourable variation, has caused 

 the resemblances in question. Bearing these points in mind, we now pass on to consider 

 instances of interspecific resemblance ; after which, we shall be in a better position to appreciate 

 the theoretical considerations to which the subject gives rise. We shall find that as in other 

 sections of the animal kingdom, so in butterflies, colours are seldom if ever the result of chance 

 development, except in so far as they may be said to have been developed by selection from 

 such variations of prior forms as have afforded their possessors some advantage in the struggle 

 to continue their kind. Beautiful as are so many of the colours and patterns found in 

 nature, it cannot be said, except perhaps in the case of epigamic colours, that beauty for 

 its own sake has had anything to do with their formation. In Darwin's words, ' nature 

 cares nothing for appearances except in so far as they are useful to any being.' Colour, 

 though only a sensation perceptible to our senses, and not a phenomenon possessed of a 

 material existence, is exhibited by all visible creatures, and is the property by which we 

 distinguish their form and outward characteristics. The beautiful adaptations which we see 

 around us are not the often quoted ' provisions of nature '. Nature's only provision is the 

 tendency to vary. We see the survivials, but the inappropriate variations, which form the 

 overwhelming majority, have been ruthlessly destroyed. They are extinct. The goal is 

 perfection of adaptation, and the penalty for lack of success is destruction. The patterns 

 of butterflies' wings, once regarded with merely interested admiration, have become, in 

 fulfilment of Bates's foreshadowing, the pages on which we can read the past history of the 

 everlasting conflict between the hunter and the hunted, and the complicated process by 

 which new forms have adapted themselves to changed and changing circumstances. 



