243 [Octoljer, 



"Polymorphism in a group of Mimetic Butterflies of the Ethiopian 

 Ntmphaline Genus Pseudacr^a," by E. B. Poulton, D.Sc, M.A., F.K.S., 

 Hope Professor in the University of Oxford. " Nature/' Vol. XC, pp. 36^ 37 : 

 September 12th, 1912. 



Under the above title Professor Poulton has communicated to our contem- 

 porary a paper bearing on our science of such importance and interest as to 

 fully justify a brief resume in our own pages. 



About two years ago Dr. Karl Jordan, in studying the 3 genital arma- 

 tures of the well-known genus of butterflies, J'sciidacrsea, found that those 

 of the group made up by the "West African P. eurytus, L., and its allies, 

 with rogersi, Trimen, from Mombasa, imitator, Trimen, from Natal, and three 

 forms from Uganda, were in all respects practically identical. All these 

 forms are mimics of species of the Acrjeine genus Planema, and in the case 

 of those observed at Entebbe, Uganda, by Mr. C. A, Wiggins, where Pseu- 

 dacrsea hobleyi, Neave, is in both sexes a beautiful mimic of the brightly 

 coloured and sexually dimorphic Planema macarista, E. M. Sharpe, and l^oth 

 sexes of the less conspicuous Ps. terra, Neave, and Ps. ohscura, Neave, bear an 

 equally close resemblance to the sexually monomorphic PI. tellus, Auriv., and PI. 

 paraqea, Gr. Sm., a very remarkable and complicated example of polymorphism 

 in the former genus is indicated. Two specimens sent by Mr. Wiggins from 

 Entebbe — a <? of Ps. terra with a pattern approaching that of hobleyi S , and a 

 ? hobleyi bearing the mimetic colours of the (? of the same form, lend strong 

 support to the identity of these so-called " species," and a few further specimens 

 corroborating this view were received after the researches of Dr. Jordan and 

 Mr. Wiggins were communicated to the Entomological Congress at Brussels in 

 1910. 



On the whole at Entebbe, Ps. hobleyi (the commonest form) and terra were 

 found to be wonderfully constant, the third, obscura, being rare. In the islands 

 of the north-west of the Victoria Nyanza, Dr. G. H. Carpenter iound the Planema 

 models rare (perhaps owing to the comparative paucity of forest), and the 

 mimics relatively abundant, terra being common and obscura plentiful, but 

 transitional forms are of very frequent occurrence. Moreover, Dr. Carpenter 

 on several occasions observed the ^ pursuing a ? of one of these mimetic forms 

 of entirely different pattern. In the collections made in 1911-12 by 

 Mr. S. A. Neave over a wide area in the Uganda Protectorate, male-coloured 

 9 's of Ps. hobleyi were found to be x-elatively much commoner than within the 

 Entebbe district, where the sexually dimorphic PI. macarista is much more 

 plentiful than the more widely spread PI. poggei, Dewitz, both sexes of which 

 resemble the ^ of macarista. 



This evidence strongly supports Dr. Jordan's views as to the specific identity 

 of these forms, and would appear to involve the necessity of sinking at least a 

 dozen " species " of Pseudacrsea as geographical and polymoi-phic " races " of the 

 old Linnean P. eurytus. But such far-reaching conclusions required before 

 acceptance the final test furnished by breeding. This test has now been 

 supplied by Dr. Carpenter, who observed at Bugalla Island, Victoria Nyanza, a 



