BUTTERFLIES AS REGISTERS OF CHANGE 53 



believe, that if we could wake up In say a thousand 

 years, we should be able to detect changes in the pat- 

 terns of some butterflies. Although I am afraid the 

 advance of science is not likely to be sufficiently rapid in 

 our time for me to hold out any prospect of such an 

 experience for any of you, there is every reason why we 

 should afford this opportunity to posterity. A critical 

 examination of the fragments of many species of butter- 

 flies captured over ninety years ago by Burchell in South 

 Africa, and gnawed to pieces during his Brazilian travels 

 from 1825 to 1830, renders it probable, nay, almost cer- 

 tain, that with moderate care, insect pigments will endure 

 for an indefinite period in our museums. One important 

 justification for the great and permanent outlay required 

 to bring together and maintain large collections of insects 

 is, that we are allowing our successors the chance of 

 detecting and measuring the rate of specific change.^ 

 And, as I have already said, for this purpose the Lepl- 

 doptera stand pre-eminent. 



For the purpose of the inquiry this evening, our 



quite unknown, but to have also established themselves in the fresh area. 

 This is a good case, as Durban has had, for the last twenty-five years 

 at least, a number of keen collectors of Lepidoptera, whom such con- 

 spicuous forms could not possibly have escaped had they inhabited the 

 neighbourhood. Besides these species, the last butterfly that my friend 

 and collaborator, the late Colonel Bowker, sent to me (1898) was the 

 large and extremely conspicuous black-and-white Acraea saiis, which he 

 took at IMalvern, near Durban. This is the only example known to me 

 to have occurred in Natal ; but Bowker, who noted the resemblance on 

 the wing to Papilio ?Jiora}iia, wrote that he had seen one other for certain, 

 and thought that he might very possibly have passed over more examples 

 for the common Papilio named. This last case is of special interest 

 (should it prove one of extended range like the three mentioned), because 

 the Acraeae are so exceptionally slow-flying and gregarious, that they must 

 spread very slowly indeed into fresh areas.' 



^ Karl Jordan argues with great force in favour of specialization in this 

 direction by our museums. (See Novitates Zoologicae, vol. iii, December 

 1896, pp. 431-3.) The Burchell collection from Brazil was made between 

 1825 and 1830, and is therefore only seventy-six to eighty-one years old, 

 but the species are numerous, and often represented by long series. Miss 

 Cora B. Sanders' account of the Iihomiine, Danaine and Satyrine butterflies 

 contains evidence that certain species have undergone change of form or 

 of distribution. See Amials ami JIagazine of Natural History^ 1904, 



PP- 305-23, 356-71. 



