O'OGO'NIUM (Neo-Lat., from Gk. kjo-yoveip, ougonein, to lay eggs, from 436v, don, egg + yovh, !low', generation). An organ in the algae and fungi (thallophytcs) which develops the eggs (oospheres), hence the female sex organ. It is gen erally a single cell, but may hear accessory struc tures. The 05gonium of the alga• was derived from a cell producing unditl•erentiated gametes (sex cells). In the process of sexual evolution sim ilar• gametes became differentiated into eggs and sperms; now the structure bearing the eggs is called the o5gonium, and that developing the sperms ('antherozoids') the antheridium. The simplest and most priinitive oiigonia probably contained several eggs, although there are not now• many illustrations of such conditions among the alga. That is to say, the evolutionary ten dency in the development of o0gonia is to reduce the number of eggs until all of the protoplasm is devoted to one. Such highly differentiated oiigo
Ma are well illustrated in Voneheria, tEdogo nhim, and Volvox. ('tiara and Coleoelnete pre sent further c•nmrplleatious in the form of fila talents that invest the cell containing the egg with a protective covering. The obgonia of fungi are in general similar to those of alga., and indeed are believed in many cases to be direetl• derived from them. They mire found chiefly in the group of the PIycomnycetes, which is closely related to the alga•. but homologous structures :a•c found in the Ascomycetes, although they generally hear the name of ascogonium or archicarp. The best illustrations of oogonia in the fungi are fur nished by the IN.:Ito]. molds (Salm•olegniales). and such well-known genera as Ailing() (Cystopusl. Pythium. and Peronospora.