the naturalist on the river amazons-第89部分

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exuberance　of　the　vegetation；　the　varied　nature　of　the　land；　the　perennial　warmth　and　humidity　of　the　climate。　But　no　description　can　convey　an　adequate　notion　of　the　beauty　and　diversity　in　form　and　colour　of　this　class　of　insects　in　the　neighbourhood　of　Ega。　I　paid　special　attention　to　them；　having　found　that　this　tribe　was　better　adapted　than　almost　any　other　group　of　animals　or　plants　to　furnish　facts　in　illustration　of　the　modifications　which　all　species　undergo　in　nature；　under　changed　local　conditions。　This　accidental　superiority　is　owing　partly　to　the　simplicity　and　distinctness　of　the　specific　character　of　the　insects；　and　partly　to　the　facility　with　which　very　copious　series　of　specimens　can　be　collected　and　placed　side　by　side　for　comparison。　The　distinctness　of　the　specific　characters　is　due　probably　to　the　fact　that　all　the　superficial　signs　of　change　in　the　organisation　are　exaggerated；　and　made　unusually　plain　by　affecting　the　framework；　shape；　and　colour　of　the　wings；　which；　as　many　anatomists　believe；　are　magnified　extensions　of　the　skin　around　the　breathing　orifices　of　the　thorax　of　the　insects。　These　expansions　are　clothed　with　minute　feathers　or　scales；　coloured　in　regular　patterns；　which　vary　in　accordance　with　the　slightest　change　in　the　conditions　to　which　the　species　are　exposed。　It　may　be　said；　therefore；　that　on　these　expanded　membranes　Nature　writes；　as　on　a　tablet；　the　story　of　the　modifications　of　species；　so　truly　do　all　changes　of　the　organisation　register　themselves　thereon。　Moreover；　the　same　colour…patterns　of　the　wings　generally　show；　with　great　regularity；　the　degrees　of　blood…relationship　of　the　species。　As　the　laws　of　Nature　must　be　the　same　for　all　beings；　the　conclusions　furnished　by　this　group　of　insects　must　be　applicable　to　the　whole　organic　world；　therefore；　the　study　of　butterflies　creatures　selected　as　the　types　of　airiness　and　frivolity　instead　of　being　despised；　will　some　day　be　valued　as　one　of　the　most　important　branches　of　Biological　science。

Before　proceeding　to　describe　the　ants；　a　few　remarks　may　be　made　on　the　singular　cases　and　cocoons　woven　by　the　caterpillars　of　certain　moths　found　at　Ega。　The　first　that　may　be　mentioned　is　one　of　the　most　beautiful　examples　of　insect　workmanship　I　ever　saw。　It　is　a　cocoon；　about　the　size　of　a　sparrow's　egg；　woven　by　a　caterpillar　in　broad　meshes　of　either　buff　or　rose…coloured　silk；　and　is　frequently　seen　in　the　narrow　alleys　of　the　forest；　suspended　from　the　extreme　tip　of　an　outstanding　leaf　by　a　strong　silken　thread　five　or　six　inches　in　length。　It　forms　a　very　conspicuous　object；　hanging　thus　in　mid…air。　The　glossy　threads　with　which　it　is　knitted　are　stout；　and　the　structure　is　therefore；　not　liable　to　be　torn　by　the　beaks　of　insectivorous　birds；　while　its　pendulous　position　makes　it　doubly　secure　against　their　attacks；　the　apparatus　giving　way　when　they　peck　at　it。　There　is　a　small　orifice　at　each　end　of　the　egg…shaped　bag；　to　admit　of　the　escape　of　the　moth　when　it　changes　from　the　little　chrysalis　which　sleeps　tranquilly　in　its　airy　cage。　The　moth　is　of　a　dull　slatey　colour；　and　belongs　to　the　Lithosiide　group　of　the　silk…worm　family　（Bombycidae）。　When　the　caterpillar　begins　its　work；　it　lets　itself　down　from　the　tip　of　the　leaf　which　it　has　chosen　by　spinning　a　thread　of　silk；　the　thickness　of　which　it　slowly　increases　as　it　descends。　Having　given　the　proper　length　to　the　cord；　it　proceeds　to　weave　its　elegant　bag；　placing　itself　in　the　centre　and　spinning　rings　of　silk　at　regular　intervals；　connecting　them　at　the　same　time　by　means　of　cross　threads　…　so　that　the　whole；　when　finished；　forms　a　loose　web；　with　quadrangular　meshes　of　nearly　equal　size　throughout。　The　task　occupies　about　four　days：　when　finished；　the　enclosed　caterpillar　becomes　sluggish；　its　skin　shrivels　and　cracks；　and　there　then　remains　a　motionless　chrysalis　of　narrow　shape；　leaning　against　the　sides　of　its　silken　cage。

Many　other　kinds　are　found　at　Ega　belonging　to　the　same　cocoon…　weaving　family；　some　of　which　differ　from　the　rest　in　their　caterpillars　possessing　the　art　of　fabricating　cases　with　fragments　of　wood　or　leaves；　in　which　they　live　secure　from　all　enemies　while　they　are　feeding　and　growing。　I　saw　many　species　of　these；　some　of　them　knitted　together；　with　fine　silken　threads；　small　bits　of　stick；　and　so　made　tubes　similar　to　those　of　caddice…worms；　others　（Saccophora）　chose　leaves　for　the　same　purpose；　forming　with　them　an　elongated　bag　open　at　both　ends；　and　having　the　inside　lined　with　a　thick　web。　The　tubes　of　full…　grown　caterpillars　of　Saccophora　are　two　inches　in　length；　and　it　is　at　this　stage　of　growth　that　I　have　generally　seen　them。　They　feed　on　the　leaves　of　Melastoniae；　and　as　in　crawling；　the　weight　of　so　large　a　dwelling　would　be　greater　than　the　contained　caterpillar　could　sustain；　the　insect　attaches　the　case　by　one　or　more　threads　to　the　leaves　or　twigs　near　which　it　is　feeding。

Foraging　AntsMany　confused　statements　have　been　published　in　books　of　travel；　and　copied　in　Natural　History　works；　regarding　these　ants；　which　appear　to　have　been　confounded　with　the　Sauba；　a　sketch　of　whose　habits　has　been　given　in　the　first　chapter　of　this　work。　The　Sauba　is　a　vegetable　feeder；　and　does　not　attack　other　animals；　the　accounts　that　have　been　published　regarding　carnivorous　ants　which　hunt　in　vast　armies；　exciting　terror　wherever　they　go；　apply　only　to　the　Ecitons；　or　foraging　ants；　a　totally　different　group　of　this　tribe　of　insects。　The　Ecitons　are　called　Tauoca　by　the　Indians；　who　are　always　on　the　look…out　for　their　armies　when　they　traverse　the　forest；　so　as　to　avoid　being　attacked。　I　met　with　ten　distinct　species　of　them；　nearly　all　of　which　have　a　different　system　of　marching；　eight　were　new　to　science　when　I　sent　them　to　England。　Some　are　found　commonly　in　every　part　of　the　country；　and　one　is　peculiar　to　the　open　campos　of　Santarem；　but；　as　nearly　all　the　species　are　found　together　at　Ega；　where　the　forest　swarmed　with　their　armies；　I　have　left　an　account　of　the　habits　of　the　whole　genus　for　this　part　of　my　narrative。　The　Ecitons　resemble；　in　their　habits；　the　Driver　ants　of　Tropical　Africa；　but　they　have　no　close　relationship　with　them　in　structure；　and　indeed　belong　to　quite　another　sub…group　of　the　ant…tribe。

Like　many　other　ants；　the　communities　of　Ecitons　are　composed；　besides　males　and　females；　of　two　classes　of　workers；　a　large…　headed　（worker…major）　and　a　small…headed　（worker…minor）　class。　the　large…heads　have；　in　some　species；　greatly　lengthened　jaws；　the　small…heads　have　jaws　always　of　the　ordinary　shape；　but　the　two　classes　are　not　sharply…defined　in　structure　and　function；　except　in　two　of　the　species。　There　is　in　all　of　them　a　little　difference　among　the　workers　regarding　the　size　of　the　head；　but　in　some　species　this　is　not　sufficient　to　cause　a　separation　into　classes；　with　division　of　labour；　in　others；　the　jaws　are　so　monstrously　lengthened　in　the　worker…majors；　that　they　are　incapacitated　from　taking　part　in　the　labours　which　the　worker…　minors　perform；　and　again；　in　others　the　difference　is　so　great　that　the　distinction　of　classes　becomes　complete；　one　acting　the　part　of　soldiers；　and　the　other　that　of　workers。　The　peculiar　feature　in　the　habits　of　the　Eciton　genus　is　their　hunting　for　prey　in　regular　bodies；　or　armies。　It　is　this　which　chiefly　distinguishes　them　from　the　genus　of　common　red　stinging…ants；　several　species　of　which　inhabit　England；　whose　habit　is　to　search　for　food　in　the　usual　irregular　manner。　All　the　Ecitons　hunt　in　large　organised　bodies；　but　almost　every　species　has　its　own　special　manner　of　hunting。

Eciton　rapax。One　of　the　foragers；　Eciton　rapax；　the　giant　of　its　genus；　whose　worker…majors　are　half…an…inch　in　length；　hunts　in　single　file　through　the　forest。　There　is　no　division　into　classes　amongst　its　workers；　although　the　difference　in　size　is　very　great；　some　being　scarcely　one…half　the　length　of　others。　The　head　and　jaws；　however；　are　always　of　the　same　shape；　and　a　gradation　in　size　is　presented　from　the　largest　to　the　smallest；　so　that　all　are　able　to　take　part　in　the　common　labours　of　the　colony。　The　chief　employment　of　the　species　seems　to　be　plundering　the　nests　of　a　large　and　defenseless　ant　of　another　genus　（Formica）；　whose　mangled　bodies　I　have　often　seen　in　their　possession　as　they　were　marching　away。　The　armies　of　Eciton　rapax　are　never　very　numerous。

Eciton　legionis。Another　species；　E。　legionis；　agrees　with　E。　rapax　in　having　workers　not　rigidly　divisible　into　two　classes；　but　it　is　much　smaller　in　size；　not　differing　greatly；　in　this　respect；　from　our　common　English　red　ant　（Myrmica　rubra）；　which　it　also　resembles　in　colour。　The　Eciton　legionis　lives　in　open　places；　and　was　seen　only　on　the　sandy　campos　of　Santarem。　　The　movement　of　its　hosts　were；　therefore；　much　more　easy　to　observe　than　those　of　all　other　kinds；　which　inhabit　solely　the　densest　thickets；　its　sting　and　bite；　also；　were　less　formidable　than　those　of　other　species。　The　armies　of　E。　legionis　consist　of　many　thousands　of　individuals；　and　move　in　rather　broad　columns。　They　are　just　as　quick　to　break　line；　on　being　disturbed；　and　attack　hurriedly　and　furiously　any　intruding　object；　as　the　other　Ecitons。　The　species　is　not　a　common　one；　and　I　seldom　had　good　opportunities　to　watch　its　habits。　The　first　time　I　saw　an　army　was　one　evening　near　sunset。　The　column　consisted　of　two　trains　of　ants；　moving　in　opposite　directions；　one　train　empty…handed；　the　other　laden　with　the　mangled　remains　of　insects；　chiefly　larvae　and　pupae　of　other　ants。　I　had　no　difficulty　in　tracing　the　line　to　the　spot　from　which　they　were　conveying　their　booty：　this　was　a　low　thicket；　the　Ecitons　were　moving　rapidly　about　a　heap　of　dead　leaves；　but　as　the　short　tropical　twilight　was　deepening　rapidly；　and　I　had　no　wish　to　be　benighted　on　the　lonely　campos；　I　deferred　further　examination　until　the　next　day。

On　the　following　morning；　no　trace　of　ants　could　be　found　near　the　place　where　I　had　seen　them　the　preceding　day；　nor　were　there　signs　of　insects　of　any　description　in　the　thicket；　but　at　the　distance　of　eighty　or　one　hundred　yards；　I　came　upon　the　same　army；　engaged；　evidently；　on　a　razzia　of　a　similar　kind　to　that　of　the　previous　even