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The requested URL /mbrowse/msdb/OriginOfSpecies/description/is/As+allied+or+representative+species,+when+inhabiting+a+continuous+area,+are+generally+distributed+in+such+a+manner+that+each+has+a+wide+range,+with+a+comparatively+narrow+neutral+territory+between+them,+in+which+they+become+rather+suddenly+rarer+and+rarer;+then,+as+varieties+do+not+essentially+differ+from+species,+the+same+rule+will+probably+apply+to+both;+and+if+we+take+a+varying+species+inhabiting+a+very+large+area,+we+shall+have+to+adapt+two+varieties+to+two+large+areas,+and+a+third+variety+to+a+narrow+intermediate+zone. The+intermediate+variety,+consequently,+will+exist+in+lesser+numbers+from+inhabiting+a+narrow+and+lesser+area;+and+practically,+as+far+as+I+can+make+out,+this+rule+holds+good+with+varieties+in+a+state+of+nature. I+have+met+with+striking+instances+of+the+rule+in+the+case+of+varieties+intermediate+between+well-marked+varieties+in+the+genus+Balanus. [[[[[images/balanus.jpg|balanus]]]]] And+it+would+appear+from+information+given+me+by+Mr.+Watson,+[[Asa+Gray|Dr.+Asa+Gray]],+and+[[Thomas+Vernon+Wollaston|Mr.+Wollaston]],+that+generally,+when+varieties+intermediate+between+two+other+forms+occur,+they+are+much+rarer+numerically+than+the+forms+which+they+connect. [[[[[images/Asa+Gray.jpg|Asa+Gray]]]]] [[[[[images/Thomas+Vernon+Wollaston.jpg|Thomas+Vernon+Wollaston]]]]] Now,+if+we+may+trust+these+facts+and+inferences,+and+conclude+that+varieties+linking+two+other+varieties+together+generally+have+existed+in+lesser+numbers+than+the+forms+which+they+connect,+then+we+can+understand+why+intermediate+varieties+should+not+endure+for+very+long+periods:-+why,+as+a+general+rule,+they+should+be+exterminated+and+disappear,+sooner+than+the+forms+which+they+originally+linked+together./ was not found on this server.