[Development of parasitism in Nematoda and formation of host-parasite relationships].

Nowadays the developmental process of parasitism within the nematodes of animals and plants also takes place. Rhabditida group coming from the soil saprophytic forms is an example of such evolutionary process in statu nascendi. The conditions and ways towards the close relationships between two organisms, leading from the commensalism and facultative parasitism to the obligatory one have been presented.