OBYDOS TO MANAOS 



177 



and the neighbouring countries, H. Melpomene has been 

 the selected form ; in the lower and more humid regions 

 of the Amazons, H. Thelxiope has been preferred. An 

 existing proof of this perfect adaptation is shown by the 

 swarming abundance of the species ; the derivation of 

 H. Thelxiope from H. Melpomene is made extremely- 

 probable by the existence of a complete series of con- 

 necting links ; and lastly, its permanent establishment 

 is made evident by its refusal to intercross with its parent 

 form, or revert to its former shape when brought by 

 natural redistribution into contact with it ^. 



CHAPTER VII 



THE LOWER AMAZONS OBYDOS TO MANAOS, OR THE 



BARRA OF THE RIO NEGRO 



A TRADER of Obydos, named Penna, was about proceeding 

 in a cuberta laden with merchandise to the Rio Negro, 

 intending to stop frequently on the road ; so I bargained 

 with him for a passage. He gave up a part of the toldo, 

 or fore-cabin as it may be called, and here I slung my 



^ If this explanation of the derivation of Heliconius Thelxiope 

 be true, the origination by natural process of a host of now 

 distinct allied species of this genus, as well as, in fact, all other 

 genera containing numerous closely related species, will have 

 to be admitted. A species allied to H. Thelxiope, namely, 

 H. Vesta, seems to have been derived also from H. Melpomene, 

 for amongst the numerous varieties already mentioned are 

 many examples intermediate between the two. There is this 

 difference, however, between H. Thelxiope and H. Vesta : 

 the former is confined in its range to the Amazons valley, 

 whilst H. Vesta extends beyond this region over Guiana and 

 the central valleys of the Andes ; it seems, therefore, to have 

 acquired a power of adaptation to a much wider diversity of 

 local conditions. Insects seem to be well adapted to furnish 

 data in illustration of this interesting but difficult subject. This 

 arises chiefly from the ease with which ample suites of specimens 

 can be obtained for comparison from many points in the areas 

 of distribution, both of species and varieties. It is scarcely 

 necessary to add that the conclusions thus arrived at will apply 

 to all organic beings. 



M 



