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For instance, are a dark and a light form whicli occur together 

 the same as a dark and a light form which are geographically 

 separate ? Staudinger and many other Lepidopterists have 

 given an affirmative answer. In Staudinger's Catalogue of 

 Palaearctic Lepidoptera many forms are designated as " var. 

 et ab.," i. e. they are considered to be individual aberrations 

 in one place which have developed into geographical varieties 

 in another. Looking superficially at collections it appears 

 indeed to be so. But appearances are frequently misleading. 

 The true bearing of a problem, whether in science, politics, 

 economics or ethics, is more easily perceived, if the problem 

 is pursued to its logical extreme. I will give some instances 

 by way of illustration. The two specimens of the Geometrid 

 Triphosa duhitata, both from Tring, differ in the one being 

 paler than the other. If this difference became so normal in 

 British duhitata that we had only dark specimens and pale 

 specimens, development progressing in the same direction 

 would result in well-marked dimorphism and no more ; the 

 dark form and the pale one would contrast strongly, but would 

 nevertheless still form an interbreeding community. Comj)are 

 now a Chinese specimen with the European ones. The Chinese 

 examples are so similar to them that they have not received a 

 name; they are, however, characterised by some slight 

 structural difference in the genitalia. The geographical 

 separation is here accompanied by a structural separation. 

 What would be the result if this line of development was 

 carried on ? The other Lepidoptera on the slide will give the 

 answer. They are both from the Oriental Region and taken 

 quite at random from my collection, being selected for no 

 other reason but the wide distribution assigned to them and, 

 as we thought, the absence of any conspicuous geographical 

 (distinctions. As it happens, the outward appearance has 

 proved deceptive. The Geometrid Nobilia turbata is said 

 to occur from India to New Guinea; the three specimens 

 figured show some very slight diSerences, but these are so 

 .fluctuating in a series that all the specimens stand in collections 

 Tunder one name. An examination of the structure, however, 

 proves that there are an Indian, a Malayan and a Papuan 

 form, so different that interbreeding would be difficult. The 



