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in animals, the formation of several embryos (twins, triplets) from a single zygote. Monovular offspring are always of the same sex. A distinction is made between specific polyembryony (normally characteristic of a given species) and sporadic, or occasional, polyembryony. Specific polyembryony characterizes some bryozoans, parasitic hymenopterans and strepsipterans, and armadillos. A striking example is the formation from one zygote of as many as 3,000 larvae in flies of the genus Litomastix. In the armadillo Dasypus hybridus Desmarest, seven to nine embryos, each having its own amnion but sharing a common chorion, develop from a single ovum. Sporadic polyembryony is observed in all animals, but it is especially frequent in some hydrozoan polyps and earthworms. In vertebrates it results from the division of the embryo into several parts, usually before or at the onset of gastrulation. In human sporadic polyembryony, two to five offspring of the same sex are born. Polyembryony has been produced experimentally in many animals by various means.
REFERENCESKanaev, I. I. Bliznetsy. Moscow-Leningrad, 1959.
Ivanova-Kazas, O. M. “Poliembrioniia u zhivotnykh.” Arkhiv anatomii, gistologii i embriologii, 1965, vol. 48, issue 3.
Tokin, B. P. Obshchaia embriologiia [2nd ed.]. Moscow 1970.
A. V. IVANOV and K. M. KURNOSOV
In plants, polyembryony is the formation of several embryos in a single seed. They may arise in a single embryo sac (true polyembryony) or in different ones (false polyembryony). With true polyembryony, several embryos develop from a single zygote as a result of the zygote’s irregular division (for example, in some tulips) or as a result of delamination of the proembryo or the proembryo’s apical cell (in the European yellow water lily). They may also develop from cells of the suspensor (in Lobelia). Often in true polyembryony the embryo arises from one or two synergids (in iris, lily, and mimosa) or antipodes (Allium odorum). Additional embryos may arise without fertilization from cells of the nucellus and the integuments. With false polyembryony, the embryo is formed either as a result of development of several embryo sacs in the ovule (strawberry, pyrethrum) or the development of not only one of the four megaspores, as usual, but of several (in lilies and lady’s mantle). It may also form owing to the development of supplementary aposporous embryo sacs (from vegetative cells) and a normal sac (in hawkweed and wormwoods).
REFERENCESMaheshwari, P. Embriologiia pokrytosemennykh. Moscow, 1954. (Translated from English.)
Poddubnaia-Arnol’di, V. A. Obshchaia embriologiia pokrytosemennykh rastenii. Moscow, 1964.
L. V. KUDRISHOV