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第PAGE\*MERGEFORMAT11页共NUMPAGES\*MERGEFORMAT11页 大学英语四级考试精读荟萃100篇(43):自然界中的保护色 Crypticcoloringisbyfarthecommonestuseofcolorinthestruggleforexistence.Itisemployedforthepurposeofattack(aggressiveresemblanceoranticrypticcoloring)aswellasofdefense(protectiveresemblanceorprocrypticcoloring).Thefactthatthesamemethodconcealment,maybeusedbothforattackanddefensehasbeenwellexplainedbyT.Beltwhosuggestsasanillustrationtherapidityofmovementwhichisalsomadeuseofbybothpursuerandpursued,whichissimilarlyraisedtoamaximuminbothbythegradualdyingoutoftheslowestthroughaseriesofgenerations.Crypticcoloringiscommonlyassociatedwithotheraidsinthestruggleforlife.Thuswell-concealedmammalsandbirds,whendiscovered,willgenerallyendeavortoescapebyspeedandwilloftenattempttodefendthemselvesactively.Ontheotherhand,smallanimalswhichhavenomeansofactivedefense,suchaslarge,numbersofinsects,frequentlydependuponconcealmentalone.Protectiveresemblanceisfarcommoneramonganimalsthanaggressiveresemblance,incorrespondencewiththefactthatpredaceousformsareasarulemuchlargerandmuchlessnumerousthantheirprey.InthecaseofinsectivorousVertebrataandtheirpreysuchdifferencesexistinanexaggeratedform.Crypticcoloring,whetherusedfordefenseofattack,maybeeithergeneralorspecial.Ingeneralresemblancetheanimal,inconsequenceofitscoloring,producesthesameeffectasitsenvironment,buttheconditionsdonotrequireanyspecialadaptationofshapeandoutline.Generalresemblanceisespeciallycommonamongtheanimalinhabitingsomeuniformlycoloredexpanseoftheearth'ssurface,suchasanoceanoradesert.Intheformer,animalsofallshapesarefrequentlyprotectedbytheirtransparentbluecolor,onthelatter,equallydiverseformsaredefendedbytheirsandyappearance.Theeffectofauniformappearancemaybeproducedbyacombinationoftintsinstartlingcontrast.Thustheblackandwhitestripesofthezebrablendtogetheratalittledistance,and"theirproportionissuchasexactlytomatchthepaletintwhicharidgroundpossesseswhenseenbymoonlight."Specialresemblanceisfarcommonerthangeneralandistheformwhichisusuallymetwithonth
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