OFTllK AMAZON VALLEY. 501 



those which sup])lv the most decisive resuUs arc MccltaiiUls Pohiiiniin, Itliomui Oroliiut 

 and nUnissd, CcraUniu yhionUi, and the Lycovece. The varieties of these present all the 

 dillerent c^rades hetwcen simple individual dillerenccs and well-marked local varieties or 

 races, which latter cannot be distint^uished from true species, when two or more of them 

 are found coexisting in the same locality without intercrossing;', as takes place in £lhoini<t 

 lUhiissa and its allies, and probably in Jlecfuinifis Nescea and LysinDiia. A strikini; 

 case of the production of a local variety now spread over a wide area, and uiulistin- 

 ijuishable from a true species, is alforded in Uclicoiiius Thclxiopc, to the details of which, 

 sjiven in the systematic part of this memoir, I must refer the reader. 



These species, when carefully studied, seem to me conclusively to show that many of 

 the now distinct species of IleUconidtc have arisen from local varieties, segreifated from 

 the variations of preexisting widely disseminated species; for these distinct forms or 

 species do not essentially dilFer from the undoubted varieties of the species cited. The 

 genera show dillerent degrees of suscepti])ility of change under altered local ccniditions. 

 Thus, many species of Ilclicouius {II. Rhea, Chjtki, lilcim, Vc.sta, T/ieLriopt', Aiitiochd, 

 &c.) are unchanged over the whole of the wide country which includes the areas of 

 several successive local races of many Hhonihc and Xapcodencs*. 



The process of the creation of a new species I belii^ve to be aceel(>rated in the Itho- 

 mice and allied genera by the strong tendency of the insects, when ])airing, to select 

 none but their exact counter])arts : this also enables a number of very closely allied ones 

 to exist together, (u- the representative forms to live side by side on the confines of theii- 

 areas, without amalgamating. 



The course followed by Nature in the forniation of these numerous local species, I 

 think, is clearly exhibited in Mcchauitis Folipintui, to the details of which, given in its 

 place, I must beg the reader to refer. AV(! s(>{^ here i\\v manufacture, as it were, in 

 process. The species is widely disseminated and variable. The external conditions in 

 certain localiti(!s are more favourable to one or more of the varieties th(>re existing than 

 to the others; those favoured ones, therefore, prevail over the others. AVe liiid, in this 

 most instructive case, all the stages of the process, from the commencement of th(> forma- 

 tion of a local variety (var. Efja'etisis) to the perfect segregation of one (var. Lijsimnia, 

 considered by all authors as a true species). In this species, most of the local varieties 

 are conui^eted with their parent form by individuals exhibiting all the; shades of varia- 

 tion ; and it is on this account only that we know them to be varieties, in the species 

 allied to Ithoniia Flora, the forms are in a complete state of segregation (with the exce])- 

 tion of /. Illutissa, which throws light on the rest), and therefore they are considered as 

 species ; they are, in fact, perfectly good species, like all other forms considi-red as such 

 in natural histcny. It is only by the study of variable species that we can obtain a clue 

 to the explanation of the rest. But such species must be studied in uatur(\ and with 



* These arelthomia Flora, an iiiliat)itmit of the wliole Lower .Vmnzon region (from the .\tlaiitie to the Rio Negro), 

 which is represented by /. Hipjifx/amia in Cayenne, and T. 0/ie</a, I/liniKSti, Giiiiillti, I'risci/lti, lUrduui, in ditferent 

 areas on the Upper Amazon ; Xapenr/enps Ctjrianassa, which becomes N. ailclphe on the banks of the Cnpari (Tapajos ), 

 and A'. Tunantina on tlie nortli bank of the L'p|)er Amazons; X. Iiiachin, wliieli is changed (o X sulphvrinn at 

 Bahia, and to N. Errilla, X. Coretia and .V. P/taro in different areas on tlie U|)per Amazon. Other .'•[Hcics inigbt 

 t)e adikd in confirmation. Most of the species of Ileliconius quoted are found unchanged over the collective areas 

 of all these forms of It/iomia and Xo/ieof/enrs. 



