the origin of species(物种起源)-第44节

按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！


ish　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　that　degree　of　nearness　to　each　other；　that　they　would　have　intersected　or　broken　into　each　other；　if　the　spheres　had　been　completed；　but　this　is　never　permitted；　the　bees　building　perfectly　flat　walls　of　wax　between　the　spheres　which　thus　tend　to　intersect。　Hence　each　cell　consists　of　an　outer　spherical　portion　and　of　two；　three；　or　more　perfectly　flat　surfaces；　according　as　the　cell　adjoins　two；　three　or　more　other　cells。　When　one　cell　comes　into　contact　with　three　other　cells；　which；　from　the　spheres　being　nearly　of　the　same　size；　is　very　frequently　and　necessarily　the　case；　the　three　flat　surfaces　are　united　into　a　pyramid；　and　this　pyramid；　as　Huber　has　remarked；　is　manifestly　a　gross　imitation　of　the　three…sided　pyramidal　basis　of　the　cell　of　the　hive…bee。　As　in　the　cells　of　the　hive…bee；　so　here；　the　three　plane　surfaces　in　any　one　cell　necessarily　enter　into　the　construction　of　three　adjoining　cells。　It　is　obvious　that　the　Melipona　saves　wax　by　this　manner　of　building；　for　the　flat　walls　between　the　adjoining　cells　are　not　double；　but　are　of　the　same　thickness　as　the　outer　spherical　portions；　and　yet　each　flat　portion　forms　a　part　of　two　cells。　
Reflecting　on　this　case；　it　occurred　to　me　that　if　the　Melipona　had　made　its　spheres　at　some　given　distance　from　each　other；　and　had　made　them　of　equal　sizes　and　had　arranged　them　symmetrically　in　a　double　layer；　the　resulting　structure　would　probably　have　been　as　perfect　as　the　comb　of　the　hive…bee。　Accordingly　I　wrote　to　Professor　Miller；　of　Cambridge；　and　this　geometer　has　kindly　read　over　the　following　statement；　drawn　up　from　his　information；　and　tells　me　that　it　is　strictly　correct：…　
If　a　number　of　equal　spheres　be　described　with　their　centres　placed　in　two　parallel　layers；　with　the　centre　of　each　sphere　at　the　distance　of　radius　X　/sqrt＇2＇　or　radius　X　1。41421　（or　at　some　lesser　distance）；　from　the　centres　of　the　six　surrounding　spheres　in　the　same　layer；　and　at　the　same　distance　from　the　centres　of　the　adjoining　spheres　in　the　other　and　parallel　layer；　then；　if　planes　of　intersection　between　the　several　spheres　in　both　layers　be　formed；　there　will　result　a　double　layer　of　hexagonal　prisms　united　together　by　pyramidal　bases　formed　of　three　rhombs；　and　the　rhombs　and　the　sides　of　the　hexagonal　prisms　will　have　every　angle　identically　the　same　with　the　best　measurements　which　have　been　made　of　the　cells　of　the　hive…bee。　
Hence　we　may　safely　conclude　that　if　we　could　slightly　modify　the　instincts　already　possessed　by　the　Melipona；　and　in　themselves　not　very　wonderful；　this　bee　would　make　a　structure　as　wonderfully　perfect　as　that　of　the　hive…bee。　We　must　suppose　the　Melipona　to　make　her　cells　truly　spherical；　and　of　equal　sizes；　and　this　would　not　be　very　surprising；　seeing　that　she　already　does　so　to　a　certain　extent；　and　seeing　what　perfectly　cylindrical　burrows　in　wood　many　insects　can　make；　apparently　by　turning　round　on　a　fixed　point。　We　must　suppose　the　Melipona　to　arrange　her　cells　in　level　layers；　as　she　already　does　her　cylindrical　cells；　and　we　must　further　suppose；　and　this　is　the　greatest　difficulty；　that　she　can　somehow　judge　accurately　at　what　distance　to　stand　from　her　fellow…labourers　when　several　are　making　their　spheres；　but　she　is　already　so　far　enabled　to　judge　of　distance；　that　she　always　describes　her　spheres　so　as　to　intersect　largely；　and　then　she　unites　the　points　of　intersection　by　perfectly　flat　surfaces。　We　have　further　to　suppose；　but　this　is　no　difficulty；　that　after　hexagonal　prisms　have　been　formed　by　the　intersection　of　adjoining　spheres　in　the　same　layer；　she　can　prolong　the　hexagon　to　any　length　requisite　to　hold　the　stock　of　honey；　in　the　same　way　as　the　rude　humble…bee　adds　cylinders　of　wax　to　the　circular　mouths　of　her　old　cocoons。　By　such　modifications　of　instincts　in　themselves　not　very　wonderful；　hardly　more　wonderful　than　those　which　guide　a　bird　to　make　its　nest；　I　believe　that　the　hive…bee　has　acquired；　through　natural　selection；　her　inimitable　architectural　powers。　
But　this　theory　can　be　tested　by　experiment。　Following　the　example　of　Mr　Tegetmeier；　I　separated　two　combs；　and　put　between　them　a　long；　thick；　square　strip　of　wax：　the　bees　instantly　began　to　excavate　minute　circular　pits　in　it；　and　as　they　deepened　these　little　pits；　they　made　them　wider　and　wider　until　they　were　converted　into　shallow　basins；　appearing　to　the　eye　perfectly　true　or　parts　of　a　sphere；　and　of　about　the　diameter　of　a　cell。　It　was　most　interesting　to　me　to　observe　that　wherever　several　bees　had　begun　to　excavate　these　basins　near　together；　they　had　begun　their　work　at　such　a　distance　from　each　other；　that　by　the　time　the　basins　had　acquired　the　above　stated　width　（i。e。　about　the　width　of　an　ordinary　cell）；　and　were　in　depth　about　one　sixth　of　the　diameter　of　the　sphere　of　which　they　formed　a　part；　the　rims　of　the　basins　intersected　or　broke　into　each　other。　As　soon　as　this　occurred；　the　bees　ceased　to　excavate；　and　began　to　build　up　flat　walls　of　wax　on　the　lines　of　intersection　between　the　basins；　so　that　each　hexagonal　prism　was　built　upon　the　festooned　edge　of　a　smooth　basin；　instead　of　on　the　straight　edges　of　a　three…sided　pyramid　as　in　the　case　of　ordinary　cells。　
I　then　put　into　the　hive；　instead　of　a　thick；　square　piece　of　wax；　a　thin　and　narrow；　knife…edged　ridge；　coloured　with　vermilion。　The　bees　instantly　began　on　both　sides　to　excavate　little　basins　near　to　each　other；　in　the　same　way　as　before；　but　the　ridge　of　wax　was　so　thin；　that　the　bottoms　of　the　basins；　if　they　had　been　excavated　to　the　same　depth　as　in　the　former　experiment；　would　have　broken　into　each　other　from　the　opposite　sides。　The　bees；　however；　did　not　suffer　this　to　happen；　and　they　stopped　their　excavations　in　due　time；　so　that　the　basins；　as　soon　as　they　had　been　a　little　deepened；　came　to　have　flat　bottoms；　and　these　flat　bottoms；　formed　by　thin　little　plates　of　the　vermilion　wax　having　been　left　ungnawed；　were　situated；　as　far　as　the　eye　could　judge；　exactly　along　the　planes　of　imaginary　intersection　between　the　basins　on　the　opposite　sides　of　the　ridge　of　wax。　In　par