318 Miss Cora B. Sanders on the Rhopalocera 



disks of the wings always clearer and the black borders more 

 sharply defined than D. rhoeo. J), dero is peculiar to Soutli- 

 East Brazil, and is not found in the Amazon region, where 

 the local form D. rhoeo takes its place. I have seen speci- 

 mens of D. rhoeo also from the neighbourhood of Bogota, 

 New Granada. It flies in thinned parts of the forest in 

 Ygapo, or flooded districts, in the dry season." (Trans. Linn. 

 Soc. Lond. vol. xxiii., 1862, pp. 520, 521.) 



I have quoted from Bates in full because, if his information 

 be correct, we have here certain evidence of change in a local 

 subspecific form within the narrow limits of five-and-twenty 

 years. All Burchell's specimens come from South-East 

 Brazil, and only two of them, viz. nos. 67 and 74 (PI. VI. 

 fig. 5), can be regarded, as de7'0. All the rest are examples 

 of the heavily marked yellowish hind-winged rhoeo (compare 

 figs. 6 and 7 with 5). It would be unwise to build too mucli 

 on the conclusion that a change has occurred, especially as 

 the interval cannot be more than about twenty-five years, 

 inasmuch as Bates, when he wrote in 1861, was dealing 

 with experiences which went back many years. But if 

 his statements that " dero is peculiar to South-East Brazil " 

 and that rhceo takes its place to the north be confirmed, we 

 are compelled to admit tliat a rapid change has occurred in 

 the former area and that in 1825 rhoeo was dominant there. 

 We should be obliged to regard the biological history as 

 traversing the history laid down by systematics ; for dei-o, 

 with the older name, would then be but a very modern local 

 form of the more ancestral although more recently named 

 rhoeo. Should further enquiry support Bates's statement, it 

 seems probable that synaposematic grouping has directed the 

 trend of evolution — that resemblance to more heavily 

 marked transparent Ithomiine associates in the north has 

 been an advantage which has caused the persistence of the 

 pronounced black markings of rhoeo, while dero has been 

 selected as an approach towards less heavily marked members 

 of Ithomiine groups in the south. 



Ithomiine butterflies with a general resemblance to one 

 another have a marked tendency to fly together, as Bates 

 points out in this very species [l. c. p. 521). It has already 

 been found in the case of Leucothyris phenomoe that the 

 northern part of Eastern Brazil is characterized by a more 

 heavily marked form [Burchelli) than the southern part (see 

 p. '-^15). In many other cases the tendency towards a 

 1 eduction of the black markings of transparent and black 

 Ithomiinas in South-Eastern Brazil has been shown in this 

 memoir. It was apparent in Pseudoscada ep. nr. utiUa (15), 



