THE GENUS PSEUDACRAEA. 233 



themselves in the evening. I did not try " sugar," but from various 

 indications I don't think it would have produced much result. It was 

 partly because of the dearth of other species that I was led to pay so 

 much attention to Lithostq/e i/riseata : and it is to tell the readers of 

 the Entomoluiiist's Record what little I know about that insect that I 

 have chiefly been moved to write these notes. 



The genus Pseudacraea— an extraordinary example of mimetic 

 polymorphism. 



By T. A. CHAPMAN, M.D., F.Z.S., F.E.S. 



At the Oxford Congress Prof. Poulton produced quite a dramatic 

 efiect in giving the present views as to certain species of this genus, 

 which only failed of a sensational climax, because a crucial specimen 

 would not emerge from the pupa quite in time for Dr. G. D. H. 

 Carpenter to send a telegram anent it from Bugalla on the Nyanza. 



Prof. Poulton announces, in Nature of September 12th, that the 

 telegram has since arrived, and the expected specimen settles, not 

 absolutely, but with reasonable certainty, that some dozen recognized 

 species of the genus Pseudacraea are all forms of Pseudacraea euri/tus, L., 

 a conclusion arrived at some years ago by Dr. K. .Jordan" from an 

 examination of the male appendages, but not positively asserted till 

 some breeding experiments should support so startling a fact. Space 

 will not allow of even a sketch of the mimicry by the various forms, 

 each of a different species of Plancwa, spread over a great part of 

 tropical and South Africa. It would seem that the mimic in this way 

 secures a much wider distribution than any one of its models. 



It is of interest, by the way, to note that the first definite step to 

 the recognition of this unity of many supposed distinct species was 

 taken by Dr. Jordan as a result of examinations of the male genitalia. 

 He refrained from asserting the result as proved, since though 

 differences in the genitalia show species to be distinct, identity does 

 not prove specific identity unless there is some other ground for such 

 a deduction. In the case of these Pseudacraeae, the presumption and 

 general opinion was in favour of their being distinct. Now we 

 have proof that some at least of these supposed " good" species are 

 not distinct, and the presumption is in favour of their being all one 

 species; Dr. Jordan's results are therefore decisive on this subject. 



The literature bearing on the subject is already considerable, we 

 may quote from Prof. Poulton's letter to Nature : — 



" The conclusion was a very startling one. If each mimetic 

 Pseudacraea had been confined to a single area and had interbred on its 

 margin with the Psendacraeae of surrounding areas with different 

 mimetic patterns, we should have been confronted with a more 

 remarkable and complex example than any as yet known (except 

 perhaps Papilio ilardanns), but one that raised no special difficulty. 

 Di. Jordan's discovery, however, involved far more than this : it led 

 to the remarkable conclusion that the sexually dimorphic P. Iioblei/i, 

 mimicking the sexually dimorphic Planema )iiacarisfa in the Entebbe 

 district, was the same species as the two monomorphic Pseudacr»as 

 flying in the same forests with it, viz., P. terra and P. ohscura, 



* ler Congr^s international d'Entomologie, Vol. II., p. 398. 



