Date of Award

Fall 1984

Project Type

Dissertation

Program or Major

Zoology

Degree Name

Doctor of Philosophy

Abstract

In Tubularia larynx and T. indivisa, interstitial cells proliferate in the ectoderm of the gonophore stalk and peduncle of the raceme and migrate in the endoderm to the apex of the young gonophore buds where they proliferate in the endoderm to form the entocodon and germ cell mass. Eggs are produced sequentially in the gonophores of both species. Each egg is the result of fusion of 1200-2000 cells interconnected by cytoplasmic bridges into a large complex. At the center of each complex are 15-18 morphologically similar cells, all of which begin meiosis and form germinal vesicles and are considered oocytes. Toward the end of vitellogenesis, the oocytes fuse to form a single large oocyte with only one germinal vesicle surviving and completing meiosis. The remaining cells of each complex enlarge and produce yolk, but do not develop a germinal vesicle. These cells are true nurse cells, connected by cytoplasmic bridges to the oocytes. The nurse cells are engulfed by the oocytes and transformed into shrunken cells as their cytoplasm is incorporated by the oocytes. The organization of the oocyte-nurse cell complexes is variable. As many as three oocytes in each complex have four cytoplasmic bridges. Cells with four bridges may be the result of cellular fusion as both oocytes and nurse cells in many complexes contain two nuclei. An oocyte-nurse cell complex is produced from one initial oogonium by mitotic proliferation and the subsequent complexes in each gonophore are probably from other oogonia. Older polyps of T. larynx are frequently hermaphroditic while T. indivisa is strictly dioecious.

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