Necessity and rigidly designating kind terms

Kripke claims that certainkind terms, particularly natural kind terms,are, like names, rigid designators. However,kind terms are more complicated than names aseach is connected both to a principle ofinclusion and an extension. So, there is aquestion regarding what it is that rigidlydesignating kind terms rigidly designate. Inthis paper, I assume that there are rigidlydesignating kind terms and attempt to answerthe question as to what it is that they rigidlydesignate. I then use this analysis of rigidlydesignating kind terms to show how Kripke''sreasoning regarding the necessity of `Hesperusis Phosphorus'' can be extended to statementsinvolving kind terms like `Water is H2O''and `Tigers are mammals''.