【求大神英语句子分析Fortaxonomy,orclassification,longseries,fromasinglenest,whichcontainallcastesaredesirable,toallowthedeterminationofvariationwithinspecies.请哪位大神分析一下这个句子''''''longseries在这是】

　　求大神英语句子分析

　　Fortaxonomy,orclassification,longseries,fromasinglenest,whichcontainallcastesaredesirable,toallowthedeterminationofvariationwithinspecies.请哪位大神分析一下这个句子''''''longseries在这是主语嘛?是什么含义?aredesirable为啥不是放在withinspecies后作主语的系表结构?