the conditions of existence-第5部分

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and　they　died；　but　if　the　black　pigs　eat　any　of　it；　it　did　not　hurt
them　at　all。　　Here　was　a　very　simple　case　of　natural　selection。　　A
skilful　breeder　could　not　more　carefully　develope　the　black　breed　of
pigs；　and　weed　out　all　the　white　pigs；　than　the　Paint　Root　does。

To　show　you　how　remarkably　indirect　may　be　such　natural　selective
agencies　as　I　have　referred　to；　I　will　conclude　by　noticing　a　case
mentioned　by　Mr。　Darwin；　and　which　is　certainly　one　of　the　most　curious
of　its　kind。　　It　is　that　of　the　Humble　Bee。　　It　has　been　noticed　that
there　are　a　great　many　more　humble　bees　in　the　neighbourhood　of　towns；
than　out　in　the　open　country；　and　the　explanation　of　the　matter　is
this：　the　humble　bees　build　nests；　in　which　they　store　their　honey　and
deposit　the　larvae　and　eggs。　　The　field　mice　are　amazingly　fond　of　the
honey　and　larvae；　therefore；　wherever　there　are　plenty　of　field　mice；　as
in　the　country；　the　humble　bees　are　kept　down；　but　in　the　neighbourhood
of　towns；　the　number　of　cats　which　prowl　about　the　fields　eat　up　the
field　mice；　and　of　course　the　more　mice　they　eat　up　the　less　there　are
to　prey　upon　the　larvae　of　the　beesthe　cats　are　therefore　the　INDIRECT
HELPERS　of　the　bees！*　　Coming　back　a　step　farther　we　may　say　that　the
old　maids　are　also　indirect　friends　of　the　humble　bees；　and　indirect
enemies　of　the　field　mice；　as　they　keep　the　cats　which　eat　up　the
latter！　　This　is　an　illustration　somewhat　beneath　the　dignity　of　the
subject；　perhaps；　but　it　occurs　to　me　in　passing；　and　with　it　I　will
conclude　this　lecture。

＇footnote＇　*The　humble　bees；　on　the　other　hand；　are　direct　helpers　of
some　plants；　such　as　the　heartsease　and　red　clover；　which　are
fertilized　by　the　visits　of　the　bees；　and　they　are　indirect　helpers　of
the　numerous　insects　which　are　more　or　less　completely　supported　by　the
heartsease　and　red　clover。







End