The article addresses the problem of nature of species which could be reduced to the question: Are species classes (universals) or individuals (particular things)? Reflecting on the discussion between traditionalist (e.g. Kitts and Kitts, Ruse) and proponents of a radical solution (Ghiselin, Hull) - by way of the S-A-I thesis (Species As Individuals) - we concentrate on the third possibility under which species are viewed as a hybrid category such as a ''complex particular,'' ''individualized class'' or ''event-entities'' (Supe, Ruse). My argument centers on an interchangeability of parts, and it concludes that we must distinguish three types of relation between parts and wholes: constructivist, emergent and reproductive. Thanks to this differentiation, I tend to view species as individuals, but not in the usual constructivist or emergent sense. In order to do justice to the individual character of species, a special logico-ontological structure or type-which I propose to call ''reproductive type''-needs to be devised. and Vladimír Havlík