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Show DARWlNl, M CHA 1'. subject to grca.t variation, so that. th.cre is much ~nccrta.inty as to the number of species; and varmtwns a.rc e~pccm~ly.ftcqucnt in the Planorbidm which exhibit ma.ny ccccntnc ~levmtwns from the u nal form ~f the spccies-devia.tions whiCh m~st oft.cn affect the form of tho living animal. In Mr. Ingersoll s H.eport on the Recent Mollusca of Colorado many of these extraordinary variations a.rc referred to, a.nd it is stated that n. shell (IIclisonia trivolvis) abundant in some small ponds and lakes, h:td scarcely two specimens alik~, ~nd man;r of them closely resembled other and altogether d1stmct spcc10s. The Variability of Insects. Among Insects there is a. large amount of ~ari~tion, .tho~tgh very few entomologists devote thcmsel vcs to 1ts mvest1gatwn. Onr first exa.mplcs will be taken from the late Mr. T. Vern on Vvollaston's book, On the Variation of Sfecies, and they must be considered as indications of very widespread thouo·h lir,tle noticed phenomena. He speaks of. the. curious li~tl c carabidcous beetles of the genus Notwphllus as bemg "extremely unstable both in their sculpture a~cl bu?; " of the common Calatbus mollis as having "the hmcl wmgs a.t one time ample, at another rudimentary, and a.t a t~ircl nca:·ly obsolete ; " and of the same irregularity as to the wm<rs bcmg characteristic of many Orthoptcra and of the Homopterons Fnlgoridoo. Mr. Westwood in his llfodern Clctssification ~f Jn w'ds states that " the species of Gerris, Hydrometra, aml V eli a arc mostly found perfectly apterous, though occasion<tlly with full-sized wings." It is, however, among the Lepidoptera (butterflies all<l moths) that the most numerous cases of variation have been observed, and every good collection of these insects afl'onh striking examples. I will first adduce the testimony of l\I r. Bates, who speaks of the butterflies of the Am<tzon valley exhibiting innumerable local varieties or race·, while s~m e species showed great individual variability. Of tho hcaut1ful Mechanitis Polymnia he says, that at Ega on the Upper Amazons, "it varies not only in general colour and pat~cm, but also very considerably in the shape of the wmg~, ~specially in tho male sex." Again, at St. Paulo, Ithonnn. 1 United States Geological Survey of the Territories, 187 4. IIl VARIABILITY OF SPEC rES IN A STA'l'E Oli' NATURE! 45 Orolina exhibits four distinct varieties, all occurring together, a.n~l these difl'cr not o11ly in colour but in form, one variety bomg described as having the foro wings much clon<Yatod in the male, while another is much Jaro·or and has "the hind wingl:i in the m:tlc diH'ercnt in shape." Of lleliconins Numa.ta Mr. HaLes sa.ys : "This species is so variable that it is difficult to find t.wo examples cxa.ctly alike," while "it varies in structure as well as in colours. Tho wings arc sometimes broader, sometimes narrower; rmd their edges arc simple in some cxampl s and festooned in others." Of another species of the same genus, H. melpomene, ton distinct va.rioties arc clcscril>cd all more or lei'-\. connected by intermediate forms, and fo11r of these va.rietics were obtained at one locality, Serpa on the north hank of tho Amazon. Ccratina inonia is another of these very nnstahle spceics exhibiting many local varicti . which arc, however, incomplete and connected by intormcclia.tc forms ; while tho . everal species of tho genus Lycorea all vary to such an extent as almost to link them together, .·o that Mr. Bates thinks they might all fairly he considered as varieties of one species only. Turning to tho Eastern IJemisphero we have in Papilo Scvcrus :t species which exhibits a largo amount of simple variation, in tho pre encc or absence of a palo patch on the upper wings, in the brown submarginal mark on tho lower wings, in tho form an l extent of the yellow band, and in tho size of the specimens. Tho most extreme forms, a. well as the intermediate ones, are often found in one locality ancl in company with each other. A small butterfly (Terias hocabc) ranges ~vor tho whole of tho Indian and Malayan regions to Au~traha, and everywhere exhibits great variations, many of whJC~ have bee~ described as distinct species ; but a gentleman m Austraba bred two of those distinct forms (T. hecabo and T. 1Esiopo), with several intermediates, from one batch of caterpillars found feeding together on the same plant.1 It is therefore very probable that a considerable number of supposed ·distinct species are only individual varieties. Cases of variation similar to those now adduced amonO' butterflies might be increased indefinitely, but it is as well t~ note that such important ch<Lracters as tho neumtion of the 1 P1·oceedings of the Entomological Society~~ London, 1875, p. vii. |