MIMETIC ASSOCIATIONS 79 



PRECIS RAUANA. 



Grose Smith (Junonia), Novit. Zool., v, p. 352 (1898). 

 Aurivillius (var. ? milonia), Rhop. Aeth., p. 139 (1898). 



Plate VIII, Fig. II. 



In the absence of a figure, Professor Aurivillius has placed this species under Precis 

 milonia as a probable variety. The genus Precis exhibits to a greater degree than any other 

 African butterflies the phenomenon known as seasonal dimorphism. Much light has been 

 thrown on our knowledge of this subject by the extensive and valuable experiments made 

 by G. A. K. Marshall, an account of which was given by Professor Poulton in their joint paper 

 in Trans. Ent. Soc, 1902.^ The above experimenter succeeded in breeding Precis sesamns 

 from Precis natalensis and the startling nature of this result may be gathered from the fact 

 that whilst P. natalensis is a salmon-red butterfly, P. sesamus is dark blue. Another species, 

 P. simia, was also shown to be the wet-season phase of P. antilope. Not only are the seasonal 

 forms of P. sesamus very different in appearance, but they also differ considerably in habits. 

 The wet-season or summer form natalensis frequents open spaces, whilst the sesamus form 

 prefers shady places, is very wary, and when alarmed flies off rapidly, and settles suddenly, 

 when its cryptic underside causes it to disappear. The very peculiar development in this 

 species of cryptic coloration in the dry phase and a conspicuous appearance in the summer 

 form, is the subject of a very interesting discussion by Professor Poulton in a part of the 

 paper referred to. It is to be noted that winter forms of tropical butterflies very frequently 

 exhibit a cryptic modification, especially of the underside. 



Generally the species of the genus Precis do not exhibit strong mimetic tendencies, and 

 the female of P. rauana is exceptional in showing so marked a development in the direction 

 of the model Planema poggei. The male is slightly smaller and is without the white suffusion 

 on the hind- wings. 



The remaining members of this group are the planemoides variety of the female P. dar- 

 danus, a form of Elymnias phegea, the eastern female of Acraea alciope, and the peculiar 

 semifulvescens form of Acraea johnstoni, each of which is described under a special section 

 dealing with the polymorphic forms of the respective species. The Planema poggei group 

 forms an exceedingly interesting illustration of the influence of a dominant type on the 

 surrounding forms which, through their instability and capacity for variation, have been 

 enabled to develop patterns which produce such close resemblances. Moreover, the coinci- 

 dence in geographical distribution of the group is exceedingly perfect. In West Africa we 

 find P. poggei accompanied by Ps. kiinowi, Acraea alciope aurivillii ? (two examples only 

 recorded), and probably by the corresponding form of Elymnias phegea. The first example 

 of the planemoides form of P. dardanus known to exist in collections was taken in 1873 in 

 Angola, showing that that protean butterfly had there come under the influence of the 

 model, but all these forms were rare until P. poggei was discovered in larger numbers at 

 Entebbe. There we find it accompanied by all its former mimics, but with the interesting 

 addition of Pseudacraea hobleyi and the female Precis rauana, together with the permanent 

 establishment of the eastern female of A. alciope. These facts are much too remarkable 

 to partake of the nature of coincidences, and demand some better explanation than those of 

 similarity of environment and local conditions, so commonly advanced by the opponents 

 of the mimetic theory. 



1 Five Years' Observation and Experiments on the Bionomics of S. African Insects, Marshall and Poulton, 

 Trans. Ent. Soc, 1902. Marshall's original paper appeared in Ann. and Mag. Nat. Hist. (7), vol. ii, 1898. 



