An early specimen of Aglais urticae ab. conjuncta Neuburg 1905 from Oxford University Museum collection. Figured in E.B. Ford's famous book Butterflies (1945). This specimen was produced by Merrifield in a temperature experiment according to the text with plate 35, but in the main text (p.241) Ford does not seem to sure?
Frederick Merrifield (1831 – 28 May 1924) from Brighton, England was an expert on Lepidoptera, he was especially interested in the effect of temperature on the colour and patterning of butterflies, rearing larvae and pupae in controlled temperature incubators and recording the effect on the colouration of adults. Examples of his very many scientific papers on this subject are (1890) 'Systematic temperature experiments on some Lepidoptera in all their stages'. Trans. Entomol Soc. London, 131-59 and (1891) Conspicuous effects on the markings and colouring of Lepidoptera caused by exposure of the pupae to different temperature conditions. Trans Entomol Soc. London, 155-67. From Wikipedia.