THE DEVELOPMENT OF THE HERMAPHRODITIC GONAD IN 4 SPECIES OF DICYEMID MESOZOANS

The development of the functionally hermaphroditic gonad, the infusori gen, in four dicyemid species, Dicyema orientale, D. acuticephalum, D. japonicum, and D. misakiense, was studied in fixed materials with the aid of a light microscope. After an agamete (axoblast) undergoes the first division and excludes a paranucleus, the resulting cell undergoe s the second division. Afterwards, three different types of cell linea ge can be identified. (1) In D. orientale, the first oogonium is produ ced by the second division, and the axial cell of an infusorigen and t he first spermatogonium are produced by the third division. (2) In D. acuticephalum, the first oogonium is produced by the second division, the axial cell is produced by the third division, and the spermatogoni um is produced by the fourth division. The fourth division also produc es the first oogonium of another egg line. (3) In D. japonicum and D. misakiense, the first spermatogonium is produced by the second divisio n, and the axial cell and the first oogonium are produced by the third division. In all species examined, oogonia occupy the outer surface o f the axial cell and spermatogonia are incorporated into the axial cel l. In this way, the spermatogenesis proceeds within the cytoplasm of t he axial cell, Mature infusorigens of these four species consist of ab out twenty cells. The respective numbers of oocytes and spermatozoa pr oduced in each infusorigen are roughly equal in these four species.