the origin of species(物种起源)-第40部分

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ed　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　parts；　only　little　bits；　in　other　parts；　large　portions　of　a　rhombic　plate　had　been　left　between　the　opposed　basins；　but　the　work；　from　the　unnatural　state　of　things；　had　not　been　neatly　performed。　The　bees　must　have　worked　at　very　nearly　the　same　rate　on　the　opposite　side　of　the　ridge　of　vermilion　wax；　as　they　circularly　gnawed　away　and　deepened　the　basins　on　both　sides；　in　order　to　have　succeeded　in　thus　leaving　flat　plates　between　the　basins；　by　stopping　work　along　the　intermediate　planes　or　planes　of　intersection。　
Considering　how　flexible　thin　wax　is；　I　do　not　see　that　there　is　any　difficulty　in　the　bees；　whilst　at　work　on　the　two　sides　of　a　strip　of　wax；　perceiving　when　they　have　gnawed　the　wax　away　to　the　proper　thinness；　and　then　stopping　their　work。　In　ordinary　combs　it　has　appeared　to　me　that　the　bees　do　not　always　succeed　in　working　at　exactly　the　same　rate　from　the　opposite　sides；　for　I　have　noticed　half…completed　rhombs　at　the　base　of　a　just…commenced　cell；　which　were　slightly　concave　on　one　side；　where　I　suppose　that　the　bees　had　excavated　too　quickly；　and　convex　on　the　opposed　side；　where　the　bees　had　worked　less　quickly。　In　one　well…marked　instance；　I　put　the　comb　back　into　the　hive　and　allowed　the　bees　to　go　on　working　for　a　short　time　and　again　examined　the　cell；　and　I　found　that　the　rhombic　plate　had　been　completed；　and　had　become　perfectly　flat：　it　was　absolutely　impossible；　from　the　extreme　thinness　of　the　little　rhombic　plate；　that　they　could　have　affected　this　by　gnawing　away　the　convex　side；　and　I　suspect　that　the　bees　in　such　cases　stand　in　the　opposed　cells　and　push　and　bend　the　ductile　and　warm　wax　（which　as　I　have　tried　is　easily　done）　into　its　proper　intermediate　plane；　and　thus　flatten　it。　
From　the　experiment　of　the　ridge　of　vermilion　wax；　we　can　clearly　see　that　if　the　bees　were　to　build　for　themselves　a　thin　wall　of　wax；　they　could　make　their　cells　of　the　proper　shape；　by　standing　at　the　proper　distance　from　each　other；　by　excavating　at　the　same　rate；　and　by　endeavouring　to　make　equal　spherical　hollows；　but　never　allowing　the　spheres　to　break　into　each　other。　Now　bees；　as　may　be　clearly　seen　by　examining　the　edge　of　a　growing　comb；　do　make　a　rough；　circumferential　wall　or　rim　all　round　the　comb；　and　they　gnaw　into　this　from　the　opposite　sides；　always　working　circularly　as　they　deepen　each　cell。　They　do　not　make　the　whole　three…sided　pyramidal　base　of　any　one　cell　at　the　same　time；　but　only　the　one　rhombic　plate　which　stands　on　the　extreme　growing　margin；　or　the　two　plates；　as　the　case　may　be；　and　they　never　complete　the　upper　edges　of　the　rhombic　plates；　until　the　hexagonal　walls　are　commenced。　Some　of　these　statements　differ　from　those　made　by　the　justly　celebrated　elder　Huber；　but　I　am　convinced　of　their　accuracy；　and　if　I　had　space；　I　could　show　that　they　are　conformable　with　my　theory。　
Huber's　statement　that　the　very　first　cell　is　excavated　out　of　a　little　parallel…sided　wall　of　wax；　is　not；　as　far　as　I　have　seen；　strictly　correct；　the　first　commencement　having　always　been　a　little　hood　of　wax；　but　I　will　not　here　enter　on　these　details。　We　see　how　important　a　part　excavation　plays　in　the　construction　of　the　cells；　but　it　would　be　a　great　error　to　suppose　that　the　bees　cannot　build　up　a　rough　wall　of　wax　in　the　proper　position　that　is；　along　the　plane　of　intersection　between　two　adjoining　spheres。　I　have　several　specimens　showing　clearly　that　they　can　do　this。　Even　in　the　rude　circumferential　rim　or　wall　of　wax　round　a　growing　comb；　flexures　may　sometimes　be　observed；　corresponding　in　position　to　the　planes　of　the　rhombic　basal　plates　of　future　cells。　But　the　rough　wall　of　wax　has　in　every　case　to　be　finished　off；　by　being　largely　gnawed　away　on　both　sides。　The　manner　in　which　the　bees　build　is　curious；　they　always　make　the　first　rough　wall　from　ten　to　twenty　times　thicker　than　the　excessively　thin　finished　wall　of　the　cell；　which　will　ultimately　be　left。　We　shall　understand　how　they　work；　by　supposing　masons　first　to　pile　up　a　broad　ridge　of　cement；　and　then　to　begin　cutting　it　away