the origin of species(物种起源)-第39部分

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　been　observed　in　the　nests　of　F。　sanguinea。　The　slaves　are　black　and　not　above　half　the　size　of　their　red　masters；　so　that　the　contrast　in　their　appearance　is　very　great。　When　the　nest　is　slightly　disturbed；　the　slaves　occasionally　come　out；　and　like　their　masters　are　much　agitated　and　defend　their　nest：　when　the　nest　is　much　disturbed　and　the　larvae　and　pupae　are　exposed；　the　slaves　work　energetically　with　their　masters　in　carrying　them　away　to　a　place　of　safety。　Hence；　it　is　clear；　that　the　slaves　feel　quite　at　home。　During　the　months　of　June　and　July；　on　three　successive　years；　I　have　watched　for　many　hours　several　nests　in　Surrey　and　Sussex；　and　never　saw　a　slave　either　leave　or　enter　a　nest。　As；　during　these　months；　the　slaves　are　very　few　in　number；　I　thought　that　they　might　behave　differently　when　more　numerous；　but　Mr。　Smith　informs　me　that　he　has　watched　the　nests　at　various　hours　during　May；　June　and　August；　both　in　Surrey　and　Hampshire；　and　has　never　seen　the　slaves；　though　present　in　large　numbers　in　August；　either　leave　or　enter　the　nest。　Hence　he　considers　them　as　strictly　household　slaves。　The　masters；　on　the　other　hand；　may　be　constantly　seen　bringing　in　materials　for　the　nest；　and　food　of　all　kinds。　During　the　present　year；　however；　in　the　month　of　July；　I　came　across　a　community　with　an　unusually　large　stock　of　slaves；　and　I　observed　a　few　slaves　mingled　with　their　masters　leaving　the　nest；　and　marching　along　the　same　road　to　a　tall　Scotch…fir…tree；　twenty…five　yards　distant；　which　they　ascended　together；　probably　in　search　of　aphides　or　cocci。　According　to　Huber；　who　had　ample　opportunities　for　observation；　in　Switzerland　the　slaves　habitually　work　with　their　masters　in　making　the　nest；　and　they　alone　open　and　close　the　doors　in　the　morning　and　evening；　and；　as　Huber　expressly　states；　their　principal　office　is　to　search　for　aphides。　This　difference　in　the　usual　habits　of　the　masters　and　slaves　in　the　two　countries；　probably　depends　merely　on　the　slaves　being　captured　in　greater　numbers　in　Switzerland　than　in　England。　
One　day　I　fortunately　chanced　to　witness　a　migration　from　one　nest　to　another；　and　it　was　a　most　interesting　spectacle　to　behold　the　masters　carefully　carrying；　as　Huber　has　described；　their　slaves　in　their　jaws。　Another　day　my　attention　was　struck　by　about　a　score　of　the　slave…makers　haunting　the　same　spot；　and　evidently　not　in　search　of　food；　they　approached　and　were　vigorously　repulsed　by　an　independent　community　of　the　slave　species　（F。　fusca）；　sometimes　as　many　as　three　of　these　ants　clinging　to　the　legs　of　the　slave…making　F。　sanguinea。　The　latter　ruthlessly　killed　their　small　opponents；　and　carried　their　dead　bodies　as　food　to　their　nest；　twenty…nine　yards　distant；　but　they　were　prevented　from　getting　any　pupae　to　rear　as　slaves。　I　then　dug　up　a　small　parcel　of　the　pupae　of　F。　fusca　from　another　nest；　and　put　them　down　on　a　bare　spot　near　the　place　of　combat；　they　were　eagerly　seized；　and　carried　off　by　the　tyrants；　who　perhaps　fancied　that；　after　all；　they　had　been　victorious　in　their　late　combat。　
At　the　same　time　I　laid　on　the　same　place　a　small　parcel　of　the　pupae　of　another　species；　F。　flava；　with　a　few　of　these　little　yellow　ants　still　clinging　to　the　fragments　of　the　nest。　This　species　is　sometimes；　though　rarely；　made　into　slaves；　as　has　been　described　by　Mr　Smith。　Although　so　small　a　species；　it　is　very　courageous；　and　I　have　seen　it　ferociously　attack　other　ants。　In　one　instance　I　found　to　my　surprise　an　independent　community　of　F。　flava　under　a　stone　beneath　a　nest　of　the　slave…making　F。　sanguinea；　and　when　I　had　accidentally　disturbed　both　nests；　the　little　ants　attacked　their　big　neighbours　with　surprising　courage。　Now　I　was　curious　to　ascertain　whether　F。　sanguinea　could　distinguish　the　pupae　of　F。　fusca；　which　they　habitually　make　into　slaves；　from　those　of　the　little　and　furious　F。　flava；　which　they　rarely　capture；　and　it　was　evident　that　they　did　at　once　distinguish　them：　for　we　have　seen　that　they　eagerly　and　instantly　seized　the　pupae　of　F。　fusca；　whereas　they　were　much　terrified　when　they　came　across　the　pupae；　or　even　the　earth　from　the　nest　of　F。　flava；　and　quickly　ran　away；　but　in　about　a　quarter　of　an　hour；　shortly　after　all　the　little　yellow　ants　had　crawled　away；　they　took　heart　and　carried　off　the　pupae。　
One　evening　I　visited　another　community　of　F。　sanguinea；　and　found　a　number　of　these　ants　entering　their　nest；　carrying　the　dead　bodies　of　F。　fusca　（showing　that　it　was　not　a　migration）　and　numerous　pupae。　I　traced　the　returning　file　burthened　with　booty；　for　about　forty　yards；　to　a　very　thick　clump　of　heath。　whence　I　saw　the　last　individual　of　F。　sanguinea　emerge；　carrying　a　pupa；　but　I　was　not　able　to　find　the　desolated　nest　in　the　thick　heath。　The　nest；　however；　must　have　been　close　at　hand；　for　two　or　three　individuals　of　F。　fusca　were　rushing　about　in　the　greatest　agitation；　and　one　was　perched　motionless　with　its　own　pupa　in　its　mouth　on　the　top　of　a　spray　of　heath　over　its　ravaged　home。　
Such　are　the　facts；　though　they　did　not　need　confirmation　by　me；　in　regard　to　the　wonderful　instinct　of　making　slaves。　Let　it　be　observed　what　a　contrast　the　instinctive　habits　of　F。　sanguinea　present　with　those　of　the　F。　rufescens。　The　latter　does　not　build　its　own　nest；　does　not　determine　its　own　migrations；　does　not　collect　food　for　itself　or　its　young；　and　cannot　even　feed　itself：　it　is　absolutely　dependent　on　its　numerous　slaves。　Formica　sanguinea；　on　the　other　hand；　possesses　much　fewer　slaves；　and　in　the　early　part　of　the　summer　extremely　few。　The　masters　determine　when　and　where　a　new　nest　shall　be　formed；　and　when　they　migrate；　the　masters　carry　the　slaves。　Both　in　Switzerland　and　England　the　slaves　seem　to　have　the　exclusive　care　of　the　larvae；　and　the　masters　alone　go　on　slave…making　expeditions。　In　Switzerland　the　slaves　and　masters　work　together；　making　and　bringing　materials　for　the　nest：　both；　but　chiefly　the　slaves；　tend；　and　milk　as　it　may　be　called；　their　aphides；　and　thus　both　collect　food　for　the　community。　In　England　the　masters　alone　usually　leave　the　nest　to　collect　building　materials　and　food　for　themselves；　their　slaves　and　larvae。　So　that　the　masters　in　this　country　receive　much　less　service　from　their　slaves　than　they　do　in　Switzerland。　
By　what　steps　the　instinct　of　F。　sanguinea　originated　I　will　not　pretend　to　conjecture。　But　as　ants；　which　are　not　slave…makers；　will；　as　I　have　seen；　carry　off　pupae　of　other　species；　if　scattered　near　their　nests；　it　is　possible　that　pupae　originally　stored　as　food　might　become　developed；　and　the　ants　thus　unintentionally　reared　would　then　follow　their　proper　instincts；　and　do　what　work　they　could。　If　their　presence　proved　useful　to　the　species　which　had　seized　them　if　it　were　more　advantageous　to　this　species　to　capture　workers　than　to　procreate　them　the　habit　of　collecting　pupae　originally　for　food　might　by　natural　selection　be　strengthened　and　rendered　permanent　for　the　very　different　purpose　of　raising　slaves。　When　the　instinct　was　once　acquired；　if　carried　out　to　a　much　less　extent　even　than　in　our　British　F。　sanguinea；　which；　as　we　have　seen；　is　less　aided　by　its　slaves　than　the　same　species　in　Switzerland；　I　can　see　no　difficulty　in　natural　selection　increasing　and　modifying　the　instinct　always　supposing　each　modification　to　be　of　use　to　the　species　until　an　ant　was　formed　as　abjectly　dependent　on　its　slaves　as　is　the　Formica　rufescens。　
Cell…making　instinct　of　the　Hive…Bee。　I　will　not　here　enter　on　minute　details　on　this　subject；　but　will　merely　give　an　outline　of　the　conclusions　at　which　I　have　arrived。　He　must　be　a　dull　man　who　can　examine　the　exquisite　structure　of　a　comb；　so　beautifully　adapted　to　its　end；　without　enthusiastic　admiration。　We　hear　from　mathematicians　that　bees　have　practically　solved　a　recondite　problem；　and　have　made　their　cells　of　the　proper　shape　to　hold　the　greatest　possible　amount　of　honey；　with　the　least　possible　consumption　of　previous　wax　in　their　construction。　It　has　been　remarked　that　a　skilful　workman；　with　fitting　tools　and　measures；　would　find　it　very　difficult　to　make　cells　of　wax　of　the　true　form；　though　this　is　perfectly　effected　by　a　crowd　of　bees　working　in　a　dark　hive。　Grant　whatever　instincts　you　please；　and　it　seems　at　first　quite　inconceivable　how　they　can　make　all　the　necessary　angles　and　planes；　or　even　perceive　when　they　are　correctly　made。　But　the　difficulty　is　not　nearly　so　great　as　it　at　first　appears：　all　this　beautiful　work　can　be　shown；　I　think；　to　follow　from　a　few　very　simple　instincts。　
I　was　led　to　investigate　this　subject　by　Mr。　Waterhouse；　who　has　shown　that　the　form　of　the　cell　stands　in　close　relation　to　the　presence　of　adjoining　cells；　and　the　following　view　may；　perhaps；　be　considered　only　as　a　modification　of　this　theory。　Let　us　look　to　the　great　principle　of　gradation；　and　see　whether　Nature　does　not　reveal　to　us　her　method　of　work。　At　one　end　of　a　short　series　we　have　humble…bees；　which　use　their　old　cocoons　to　hold　honey；　sometimes　adding　to　them　short　tubes　of　wax；　and　likewise　making　separate　and　very　irregular　rounded　cells　of　wax。　At　the　other　end　of　the　series　we　have　the　cells　of　the　hive…bee；　placed　in　a　double　layer：　each　cell；　as　is　well　know；　is　an　hexagonal　prism；　with　the　basal　edges　of　its　six　sides　bevelled　so　as　to　join　on　to　a　pyramid；　formed　of　three　rhombs。　These　rhombs　have　certain　angles；　and　the　three　which　form　the　pyramidal　base　of　a　single　cell　on　one　side　of　the　comb；　enter　into　the　composition　of　the　bases　of　three　adjoining　cells　on　the　opposite　side。　In　the　series　between　the　extreme　perfection　of　the　cells　of　the　hive…bee　and　the　simplicity　of　those　of　the　humble…bee；　we　have　the　cells　of　the　Mexican　Melipona　domestica；　carefully　described　and　figured　by　Pierre　Huber。　The　Melipona　itself　is　intermediate　in　structure　between　the　hive　and　humble　bee；　but　more　nearly　related　to　the　latter：　it　forms　a　nearly　regular　waxen　comb　of　cylindrical　cells；　in　which　the　young　are　hatched；　and；　in　addition；　some　large　cells　of　wax　for　holding　honey。　These　latter　cells　are　nearly　spherical　and　of　nearly　equal　sizes；　and　are　aggregated　into　an　irregular　mass。　But　the　important　point　to　notice；　is　that　these　cells　are　always　made　at