D.— ZOOLOGY loi 



by an unusually large percentage of butterflies which have the upper side 

 white with a black border to the wings, as in Pieridce, even a number of 

 Blues having acquired this colour — involves one unavoidably in arguments 

 about mimicry, a subject outside this address and concerning which I 

 will say no more than that there are numerous cases of convergence in 

 appearance unexplainable to me if mimicry were not a reality. I will, 

 however, refer to a few non-mimetic illustrations of convergent develop- 

 ment in which the influence of locality is very apparent. In a number 

 of Oriental Papilios, with a tail to the hindwing, this appendage becomes 

 reduced as we proceed eastwards, and in some instances disappears 

 altogether on the Papuan islands. New Guinea has produced very 

 striking metallic coloration in two groups of animals, the Birds of 

 Paradise and the Geometrid moths Milionia. A number of butterflies 

 of the island of Celebes are large and have the forewings strongly curved. 

 The home of long-tailed Geometrid moths is South America, where also 

 occur long-tailed Riodinid butterflies similar in habits and sometimes in 

 appearance to these Geometrids. We do not always have a satisfactory 

 explanation of such convergences ; but the darker coloration of certain 

 West African butterflies as compared with their East African representa- 

 tives, and of some Sumatran forms as compared with those from Java, is 

 probably explained by the damper climate favouring the production of 

 black-brown. The wings in a number of migratory birds are shorter in 

 several Algerian subspecies than in the European ones — ^for instance, in 

 the House-Martin, the Hawfinch, Goatsucker, and others, possibly due 

 to these subspecies having to fly a shorter distance to their winter quarters 

 than the northern birds, and therefore short-winged individuals having 

 a better chance of surviving than in the case of northern migrants. 



Another point of significance revealed by collections is the frequency 

 of monomorphism in the outlying districts of polymorphic species. 

 Papilio cegeiis Don., for example, is polymorphic in New Guinea, appearing 

 in two forms of the ^ and several female-forms ; the various subspecies 

 flying in Australia and on the Moluccas have only one kind of female. 

 The polymorphic Papilio memnon L. has a monomorphic female in its 

 most northern area, Japan. The African Papilio dardanus Brown is 

 monomorphic in Madagascar and the Comoro Islands (the female being 

 but slightly different from the male), whereas on the African Continent 

 the species is not only strongly sexually dimorphic, but moreover 

 polymorphic in the female. 



The simplification from the centre of distribution outwards, indicated 

 by the examples mentioned, obtains also in some insects where the sexes 

 of the species remain monomorphic in the whole area. According to the 

 researches of Onslow,^" the conspicuously different geographical forms of 

 Papilio priamus L., the orange one inhabiting the Northern Moluccas, 

 the blue one found in New Ireland and the Solomon Islands, and the green 

 forms occurring in the interjacent countries, differ from each other (in 

 the tint of colour) in that the orange form has an orange pigment in the 

 scales, the blue form no pigment, but a structural blue, and the green 

 forms a combination of the yellow pigment with the structural blue. 

 '" Philos. Trans. Roy. Soc, B 211, p. 39 (1923). 



