darwin and modern science-第87节

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3；　1867：　　〃By　the　way；　I　cannot　but　think　that　you　push　protection　too　far　in　some　cases；　as　with　the　stripes　on　the　tiger。〃　　（〃More　Letters〃；　I。　page　283。）　　Here　too　Darwin　was　preferring　the　explanation　offered　by　Sexual　Selection　（〃Descent　of　Man〃　（2nd　edition）　1874；　pages　545；　546。）；　a　preference　which；　considering　the　relation　of　the　colouring　of　the　lion　and　tiger　to　their　respective　environments；　few　naturalists　will　be　found　to　share。　　It　is　also　shown　that　Darwin　contemplated　the　possibility　of　cryptic　colours　such　as　those　of　Patagonian　animals　being　due　to　sexual　selection　influenced　by　the　aspect　of　surrounding　nature。

Nearly　a　year　later　Darwin　in　his　letter　of　May　5；　1868？；　expressed　his　agreement　with　Wallace's　views：　　〃Expect　that　I　should　put　sexual　selection　as　an　equal；　or　perhaps　as　even　a　more　important　agent　in　giving　colour　than　Natural　Selection　for　protection。〃　　（〃More　Letters〃；　II。　pages　77；　78。）　　The　conclusion　expressed　in　the　above　quoted　passage　is　opposed　by　the　extraordinary　development　of　Protective　Resemblance　in　the　immature　stages　of　animals；　especially　insects。

It　must　not　be　supposed；　however；　that　Darwin　ascribed　an　unimportant　role　to　Cryptic　Resemblances；　and　as　observations　accumulated　he　came　to　recognise　their　efficiency　in　fresh　groups　of　the　animal　kingdom。　　Thus　he　wrote　to　Wallace；　May　5；　1867：　　〃Haeckel　has　recently　well　shown　that　the　transparency　and　absence　of　colour　in　the　lower　oceanic　animals；　belonging　to　the　most　different　classes；　may　be　well　accounted　for　on　the　principle　of　protection。〃　　（〃More　Letters〃；　II。　page　62。　　See　also　〃Descent　of　Man〃；　page　261。）　　Darwin　also　admitted　the　justice　of　Professor　E。S。　Morse's　contention　that　the　shells　of　molluscs　are　often　adaptively　coloured。　　（〃More　Letters〃；　II。　page　95。）　　But　he　looked　upon　cryptic　colouring　and　also　mimicry　as　more　especially　Wallace's　departments；　and　sent　to　him　and　to　Professor　Meldola　observations　and　notes　bearing　upon　these　subjects。　　Thus　the　following　letter　given　to　me　by　Dr　A。R。　Wallace　and　now；　by　kind　permission；　published　for　the　first　time；　accompanied　a　photograph　of　the　chrysalis　of　Papilio　sarpedon　choredon；　Feld。；　suspended　from　a　leaf　of　its　food…plant：

July　9th；　Down；　Beckenham；　Kent。

My　Dear　Wallace；

Dr　G。　Krefft　has　sent　me　the　enclosed　from　Sydney。　　A　nurseryman　saw　a　caterpillar　feeding　on　a　plant　and　covered　the　whole　up；　but　when　he　searched　for　the　cocoon　（pupa）；　was　long　before　he　could　find　it；　so　good　was　its　imitation　in　colour　and　form　to　the　leaf　to　which　it　was　attached。　I　hope　that　the　world　goes　well　with　you。　　Do　not　trouble　yourself　by　acknowledging　this。

Ever　yours

Ch。　Darwin。

Another　deeply　interesting　letter　of　Darwin's　bearing　upon　protective　resemblance；　has　only　recently　been　shown　to　me　by　my　friend　Professor　E。B。　Wilson；　the　great　American　Cytologist。　　With　his　kind　consent　and　that　of　Mr　Francis　Darwin；　this　letter；　written　four　months　before　Darwin's　death　on　April　19；　1882；　is　reproduced　here　（The　letter　is　addressed：　　〃Edmund　B。　Wilson；　Esq。；　Assistant　in　Biology；　John　Hopkins　University；　Baltimore　Md；　U。　States。〃：

December　21；　1881。

Dear　Sir；

I　thank　you　much　for　having　taken　so　much　trouble　in　describing　fully　your　interesting　and　curious　case　of　mimickry。

I　am　in　the　habit　of　looking　through　many　scientific　Journals；　and　though　my　memory　is　now　not　nearly　so　good　as　it　was；　I　feel　pretty　sure　that　no　such　case　as　yours　has　been　described　（amongst　the　nudibranch）　molluscs。　　You　perhaps　know　the　case　of　a　fish　allied　to　Hippocampus；　（described　some　years　ago　by　Dr　Gunther　in　〃Proc。　Zoolog。　Socy。〃）　which　clings　by　its　tail　to　sea…weeds；　and　is　covered　with　waving　filaments　so　as　itself　to　look　like　a　piece　of　the　same　sea…weed。　　The　parallelism　between　your　and　Dr　Gunther's　case　makes　both　of　them　the　more　interesting；　considering　how　far　a　fish　and　a　mollusc　stand　apart。　　It　would　be　difficult　for　anyone　to　explain　such　cases　by　the　direct　action　of　the　environment。I　am　glad　that　you　intend　to　make　further　observations　on　this　mollusc；　and　I　hope　that　you　will　give　a　figure　and　if　possible　a　coloured　figure。

With　all　good　wishes　from　an　old　brother　naturalist；

I　remain；　Dear　Sir；

Yours　faithfully；

Charles　Darwin。

Professor　E。B。　Wilson　has　kindly　given　the　following　account　of　the　circumstances　under　which　he　had　written　to　Darwin：　　〃The　case　to　which　Darwin's　letter　refers　is　that　of　the　nudibranch　mollusc　Scyllaea；　which　lives　on　the　floating　Sargassum　and　shows　a　really　astonishing　resemblance　to　the　plant；　having　leaf…shaped　processes　very　closely　similar　to　the　fronds　of　the　sea…weed　both　in　shape　and　in　colour。　　The　concealment　of　the　animal　may　be　judged　from　the　fact　that　we　found　the　animal　quite　by　accident　on　a　piece　of　Sargassum　that　had　been　in　a　glass　jar　in　the　laboratory　for　some　time　and　had　been　closely　examined　in　the　search　for　hydroids　and　the　like　without　disclosing　the　presence　upon　it　of　two　large　specimens　of　the　Scyllaea　（the　animal；　as　I　recall　it；　is　about　two　inches　long）。　　It　was　first　detected　by　its　movements　alone；　by　someone　（I　think　a　casual　visitor　to　the　laboratory）　who　was　looking　closely　at　the　Sargassum　and　exclaimed　'Why；　the　sea…weed　is　moving　its　leaves'！　　We　found　the　example　in　the　summer　of　1880　or　1881　at　Beaufort；　N。C。；　where　the　Johns　Hopkins　laboratory　was　located　for　the　time　being。　　It　must　have　been　seen　by　many　others；　before　or　since。

〃I　wrote　and　sent　to　Darwin　a　short　description　of　the　case　at　the　suggestion　of　Brooks；　with　whom　I　was　at　the　time　a　student。　　I　was；　of　course；　entirely　unknown　to　Darwin　（or　to　anyone　else）　and　to　me　the　principal　interest　of　Darwin's　letter　is　the　evidence　that　it　gives　of　his　extraordinary　kindness　and　friendliness　towards　an　obscure　youngster　who　had　of　course　absolutely　no　claim　upon　his　time　or　attention。　　The　little　incident　made　an　indelible　impression　upon　my　memory　and　taught　me　a　lesson　that　was　worth　learning。〃

VARIABLE　PROTECTIVE　RESEMBLANCE。

The　wonderful　power　of　rapid　colour　adjustment　possessed　by　the　cuttle…fish　was　observed　by　Darwin　in　1832　at　St　Jago；　Cape　de　Verd　Islands；　the　first　place　visited　during　the　voyage　of　the　〃Beagle〃。　　From　Rio　he　wrote　to　Henslow；　giving　the　following　account　of　his　observations；　May　18；　1832：　　〃I　took　several　specimens　of　an　Octopus　which　possessed　a　most　marvellous　power　of　changing　its　colours；　equalling　any　chameleon；　and　evidently　accommodating　the　changes　to　the　colour　of　the　ground　which　it　passed　over。　Yellowish　green；　dark　brown；　and　red；　were　the　prevailing　colours；　this　fact　appears　to　be　new；　as　far　as　I　can　find　out。〃　　（〃Life　and　Letters〃；　I。　pages　235；　236。　　See　also　Darwin's　〃Journal　of　Researches〃；　1876；　pages　6…　8；　where　a　far　more　detailed　account　is　given　together　with　a　reference　to　〃Encycl。　of　Anat。　and　Physiol。〃）

Darwin　was　well　aware　of　the　power　of　individual　colour　adjustment；　now　known　to　be　possessed　by　large　numbers　of　lepidopterous　pupae　and　larvae。　　An　excellent　example　was　brought　to　his　notice　by　C。V。　Riley　（〃More　Letters〃　II；　pages　385；　386。）；　while　the　most　striking　of　the　early　results　obtained　with　the　pupae　of　butterfliesthose　of　Mrs　M。E。　Barber　upon　Papilio　nireuswas　communicated　by　him　to　the　Entomological　Society　of　London。　　（〃Trans。　Ent。　Soc。　Lond。〃　1874；　page　519。　　See　also　〃More　Letters〃；　II。　page　403。）

It　is　also　necessary　to　direct　attention　to　C。W。　Beebe's　（〃Zoologica：　　N。Y。　Zool。　Soc。〃　Vol。　I。　No。　1；　Sept。　25；　1907：　〃Geographic　variation　in　birds　with　especial　reference　to　the　effects　of　humidity〃。）　recent　discovery　that　the　pigmentation　of　the　plumage　of　certain　birds　is　increased　by　confinement　in　a　superhumid　atmosphere。　　In　Scardafella　inca；　on　which　the　most　complete　series　of　experiments　was　made；　the　changes　took　place　only　at　the　moults；　whether　normal　and　annual　or　artificially　induced　at　shorter　periods。　　There　was　a　corresponding　increase　in　the　choroidal　pigment　of　the　eye。　　At　a　certain　advanced　stage　of　feather　pigmentation　a　brilliant　iridescent　bronze　or　green　tint　made　its　appearance　on　those　areas　where　iridescence　most　often　occurs　in　allied　genera。　　Thus　in　birds　no　less　than　in　insects；　characters　previously　regarded　as　of　taxonomic　value；　can　be　evoked　or　withheld　by　the　forces　of　the　environment。

WARNING　OR　APOSEMATIC　COLOURS。

From　Darwin's　description　of　the　colours　and　habits　it　is　evident　that　he　observed；　in　1833；　an　excellent　example　of　warning　colouring　in　a　little　South　American　toad　（Phryniscus　nigricans）。　　He　described　it　in　a　letter　to　Henslow；　written　from　Monte　Video；　Nov。　24；　1832：　　〃As　for　one　little　toad；　I　hope　it　may　be　new；　that　it　may　be　christened　'diabolicus。'　　Milton　must　allude　to　this　very　individual　when　he　talks　of　'squat　like　a　toad'；　its　colours　are　by　Werner　（〃Nomenclature　of　Colours〃；　1821）　ink　black；　vermilion　red　and　buff　orange。〃　　（〃More　Letters〃；　I。　page　12。）　　In　the　〃Journal　of　Researches〃　（1876；　page　97。）　its　colours　are　described　as　follows：　　〃If　we　imagine；　first；　that　it　had　been　steeped　in　the　blackest　ink；　and　then；　when　dry；　allowed　to　crawl　over　a　board；　freshly　painted　with　the　brightest　vermilion；　so　as　to　colour　the　soles　of　its　feet　and　parts　of