28 



INTRODUCTION. 



discs which are found on the palpi of - certain species of Carabus, 

 surrounded by a large number of minute teeth. The whole question, 

 at present, rests largely on pure hypothesis. 



Coloration. 



The colours of Coleoptera vary as much as their size and form. 

 The most brilliant are, perhaps, the BuPRESTiDiE and the 

 Cetoniid.e ; but the CiciNDELLDiE and many of the Chryso- 

 melidje and their allied groups, and many also of the Longicornia, 

 run these very close in beauty of colour. The brilliant metallic 

 colours may be either entirely structural, or else due to a com- 

 bination of structure and pigment. The structural colours of 

 Coleoptera probably belong, for the" most part, to the category of 

 interference colours, such as are seen in a soap-bubble. Colours 

 of this kind are produced by thin films of air, or of liquids of low- 

 refractive power, included between layers of a horny consistence. 

 If the films consist of air, the colour remains unaltered in dry 

 specimens ; if, how r ever, they are liquid, as the tissue dries up so 

 also do the films, and the colour disappears. This is very evident 

 in insects like the Cassidlde, which, in their native tropical 

 habitat, are among the most brilliant of beetles, and glitter like 

 large dewdrops in the sun with shining metallic or opalescent 

 colours, but in our collections present a uniformly faded ap- 

 pearance. If, however, they are kept in spirit or water, they 

 retain their colour. Such colours may even fade and be restored 

 in a living beetle, for it has been observed that a brilliant golden 

 beetle (Carabus auronitens) lost all its lustre after hybernating in 

 captivity, but regained it after drinking some water. Many 

 metallic colours are also due to diffraction (caused by white light 

 being reflected from a number of fine parallel grooves) or refraction 

 (prismatic colours). The general subject will be found discussed 

 in Professor Poulton's ' Colours of Animals ' (International Science 

 Series, pp. 1-11), to which work I am indebted for the chief part 

 of the foregoing observations. 



Mimicry and Protective Resemblance. 



In my Presidential Addresses to the Entomological Society of 

 London in 1902 and 1903 I dealt partly with the question of 

 Mimicry and Protection among the Coleoptera, a subject which 

 had been comparatively neglected in this order, although it 

 had been for a long time brought into stroug notice so far as 

 the Lepidoptera were concerned. It may perhaps be useful to 

 recapitulate briefly the chief points noticed, as observers in the 

 field will certainly be able to add a vast number of interesting facts 

 if they will only make note of them as they occur. Indeed, it is 

 only the field-workers who have really any right to speak on the 

 matter, as theorizing on possible resemblances and adaptations to 

 surroundings in museums, though often very useful, is liable to be 



