300 Professor E. B. Poulton on Mimetic Forms of 



striking example of Miillerian mimicry which it was to 

 supply. 



I. Mimetic forms o/Acrcea johnstoni, Godman. 



It is now proposed to consider the various often widely- 

 separated forms o^ johnstoni in the probable order of their 

 evolution in time, and to point out the models in each 

 case. 



(1) Acnea jolmstoni, Godm., form ^'^'^'otcina, Obetth. 

 Oberthiir (Etudes D'Entomologie : Dix-septieme Livr. : 

 Avril 1893 : PI. II, Fig. 14) considers the variety with 

 white spots in the fore-wing and a squarish pale buff 

 discal patch in the hind-wing as the typical form of the 

 species ; and it is probably more ancestral than any other. 

 It appears to be much more abundant than the buff-spotted 

 form fiavesccns, and also to have a wider range. The most 

 southern examples in tlie Hope Collection, viz. three 

 specimens sent to me by my kind friend Mr. Guy A. 

 K. Marshall from Chirinda Forest, Gazaland, in S.E. 

 Rhodesia (4000 feet), are all of this form, and it is also far 

 more numerous than any other in the Rev. K. St. Aubyn 

 Rogers' series from the Kilimanjaro district, as also in the 

 series from the Tiriki Hills on the N.E. shores of the 

 Victoria Nyanza (5100 feet) kindly given me by Mr. C. A. 

 Wiggins. 



1l\\q protcina form is an obvious and beautiful mimic of 

 Amauris alhimaculata and the white-spotted forms of 

 Amcmris eclicria. Its synaposematic sensitiveness is well 

 seen in Mr. Marshall's specimens from Chirinda in which 

 the squarish discal patch of the hind -wing is unusually 

 large, clearly as an approach to Amauris lohcngnla 

 (Plate XXII, Fig. 1), one of the dominant Danaines of 

 this locality. The discal expansion is more pronounced in 

 tlie female Acr/vct (Fig. Ih) than in the two males, one of 

 which is represented in Fig. Ice. The more perfect mimetic 

 likeness of the female is an example of the well-known and 

 widely applicable principle explained by A. R. Wallace.* 



The resemblance oi iwotcina to the Danaine model is far 

 less perfect on the under-side, although the spots of the 

 fore-wing and the patch of the hind-wing are still the 

 prominent features. The ground colour in the marginal 



* Tran8. Linn. Soc, vol. xxv, 18G6, Pt. I, 1865, p. 22. See also 

 Poulton in Linn. Soc. Jonrn. ZooL, vol. xxvi, pp. 580-582. 



