252 DARWINISM chap. 



difference, in the important character of the neuration of the 

 wings, between these butterflies, which really belong to very 

 distinct and not at all closely allied genera. Other important 

 characters are — (1) The existence of a small basal cell in the 

 hind wings of Ituna which is wanting in Thyridia ; (2) the 

 division of the cell between the veins lb and 2 of the 

 hind wings in the former genus, while it is undivided in the 

 latter ; and (3) the existence in Thyridia of scent-producing 

 tufts of hair on the upper edge of the hind wing, while in 

 Ituna these are wanting ; but in place of them are extensible 

 processes at the end of the abdomen, also emitting a powerful 

 scent. These differences characterise two marked subdivisions 

 of the Danaoid Heliconinse, each containing several distinct 

 genera; and these subdivisions are further distinguished by very 

 different forms of larvae, that to which Ituna belongs having 

 from two to four long threadlike tentacles on the back, while 

 in that containing Thyridia these are always absent. The 

 former usually feed on Asclepiadeae, the latter on Solanaceae 

 or Scrophulariaceae. 



The two species figured, though belonging to such distinct 

 and even remote genera, have acquired almost identical tints 

 and markings so as to be deceptively alike. The surface of 

 the wings is, in both, transparent yellowish, with black trans- 

 verse bands and white marginal spots, while both have similar 

 black- and white -marked bodies and long yellow antennae. 

 Dr. Miiller states that they both show a preference for the 

 same flowers growing on the edges of the forest paths. 1 



We will now proceed to give the explanation of these 

 curious similarities, which have remained a complete puzzle 

 for twenty years. Mr. Bates, when first describing them, 

 suggested that they might be due to some form of parallel 

 variation dependent on climatic influences; and I myself 

 adduced other cases of coincident local modifications of 

 colour, which did not appear to be explicable by any form 

 of mimicry. 2 But we neither of us hit upon the simple 

 explanation given by Dr. Fritz Miiller in 1879. 



His theory is founded on the assumed, but probable, 



1 From Professor Meldola's translation of Dr. F. Muller's paper, in Proc. 

 Ent. Soc. Lond., 1879, p. xx. 



2 Island Life, p. 255. 



