1901.] Mimetic Insects. 693 



WEEKLY EVENING MEETING, 

 Friday, June 7, 1901. 



His Grace The Duke of Northumberland, E.G. D.C.L. F.E.S., 

 President, in the Chair. 



Professor Raphael Meldola, F.R.S. M.B.I. 



Mimetic Insects. 



The Lecturer commenced by describing the production of colour 

 among insects by selective absorption due to pigments and by purely 

 physical structure causing interference. Images of butterflies (Cal- 

 lidryas and Morpho) illustrating the two classes of colouring were 

 thrown on the screen. The subject of iusect coloration was not 

 considered in relation to physical, chemical, or physiological causes, 

 but rather with reference to its bionomic significance, i.e. its value so 

 far as it concerned the welfare of the species. It had long been 

 familiar to naturalists that the colour and pattern, form and habit 

 were often adaptive. This adaptation to environment, apart from 

 any hypothesis, is one of the most marvellous facts presented by 

 living organisms when examined in detail. The effect of the adapta- 

 tion is concealment, whether for the purpose of enabling the insects to 

 escape from their foes, or in order to enable them to secure food by 

 approaching their prey undetected. It was convenient to distinguish 

 between protective and aggressive resemblance, although in all cases 

 it was not possible to decide off-hand without a full knowledge of 

 life-history to which class any particular case should be referred. 



Illustrations showing the harmony of colour, pattern and form 

 between insects and their surroundings were shown on the screen, 

 many examples being taken from native species at different stages in 

 their life-histories. The explanation of the adaptations considered 

 was referred to the action of natural selection, the advantage of con- 

 cealment in such cases being sufficiently obvious to warrant the 

 application of the principles of selection as laid down by Darwin 

 and Wallace. 



The Lecturer next proceeded to the consideration of those cases 

 in which the colours and markings were conspicuous, and no attempt 

 at concealment was made. These were explained also by the 

 principles of selection as applied by Wallace in his well known 

 theory of " warning colours." With these two classes of facts, colour 

 for concealment and colour for warning, it was easy to carry the 

 mind forward to true mimetic resemblances in which the species 



