LIFE CYCLE of animals — set of phases of development, or the period of life of an organism, in the course of passing to-rogo an organism becomes capable to give rise to new generation. Distinguish two main types Zh. c.: direct development, at Krom development of an animal happens without transformations, and development to digenesis, or metamorphosis (see). At direct development complication of an organism happens gradually and separate stages of its development have no big morfofunktsionalny differences. At development with metamorphosis larval stages significantly differ from adults in the morfofunktsionalny relation; their value in. c. also variously. So, larvae of butterflies or mosquitoes have the specific form and a structure of a body, a specialized respiratory organs, digestion and movement, not inherent to adult individuals. At some animals. c. includes a state fiziol, the rest which is evolutionarily developed adaptation to experience of adverse conditions of the environment for life activity (see. Anabiosis , Diapause , Hibernation ).
Duration. c. is defined by duration of development of separate phases, existence or lack of a diapause etc. At one organisms. c. comes to the end quickly, and these organisms give several generation during a season, at others. c. lasts for several years
. c. the elementary unicells it is characterized usually by alternation of sexless and sexual generations and comes to an end with cell division and formation of two affiliated. At metaphytes the main type Zh. c. it is connected with a syngenesis; the zygote, as a rule, forms one adult individual. Alternation of generations arises only as adaptation to to parasitism (see). At the same time during. c. several morphologically various phases are replaced consistently (e.g., at a bull soliter: egg — an oncosphere — the Finn — an adult tapeworm). Alternation of phases on an extent. c. many parasites is followed by change of owners — life of one generation proceeds in a body of one owner, other generation — another etc. One species of the parasitizing animals developing with obligatory change of owners at each stage of the. c. can parasitize or on the unique type of the owner, or on several close types. Quite often. c. a parasite it is in details adapted to. c. the owner.
Studying. c. various animals is of great importance for medical practice. Knowledge. c. owners and parasites allows to understand more precisely an etiology and a pathogeny of various diseases of the person and animals, gives the chance to develop effective measures of fight and prevention against these diseases. Studying of features of an annual cycle of life of a number of carriers (their phenology, number, gonotrofichesky cycles, age composition etc.) allows to choose optimum tactics and time of holding actions in each certain district, to gain the greatest effect with the minimum expense of forces and means. Studying. c. helminths formed the basis of the doctrine of K. I. Scriabin about dewormings (see) and devastation (see). Studying. c. activators and carriers of a number of infectious and invasive diseases formed the basis of the exercise E.N. Pavlovsky about natural ochagovost (see) and developments of measures of fight and prevention of many transmissible diseases (see).
Bibliography: Dogel V. A. General parasitology, L., 1962; The Course of zoology, under the editorship of B. S. Matveev, t. 1 — 2, M., 1966; Pavlovsky E. H. Guide to parasitology of the person, t. 1 — 2, M. — L., 1946 — 1948.