On the problem of variable numbers of hosts in the life-cycles of helminths.

The authors analyze the phenomena underlying the variation of host numbers in the life-cycle of several helminth species. Variation of host number in the cycle is effected by alternative shortening of the cycle (with this the cycle turns out either without or with a polyvalent obligatory host or, in rarer cases, without or with appearing of neogeny) or by facultative widening of the cycle (without or with participation of additional hosts, namely para-paratenic, paradefinitive, metaparatenic, or euparatenic hosts). The term of metaparatenic host is made precise by limitation to a "hemistadiogenous" additional host (sensu Barus and Rysavý 1977).

[Certain principles of the secondary simplication of the life cycles of helminths]. / O nekotorykh zakonomernostiakh pri vtorichnom uproshchenii zhiznennykh tsiklov gel'mintov

On the basis of the analysis of regularities accompanying the secondary simplification of the life cycles of helminths on account of the reduction in the number of the animals-hosts 8 rules have been formulated. They are based on the following important regularities. 1. At the secondary simplification of the life cycles of helminths never fall out the first intermediate host in Trematoda and the definitive host in Nematoda. This phenomenon is suggested to be called "the host stability in the life cycle". 2. Mostly often from the life cycles fall secondarily out those hosts which join in the life cycle at its first complication later. 3. The phase of the helminth having transformed into a parasitic form at the first complication of its life cycle remains the same at the secondary simplification of this cycle.