BUDDING, SEXUAL REPRODUCTION, AND DEGENERATION IN THE COLONIAL ASCIDIAN, SYMPLEGMA REPTANS

¹ Zoological Institute, Faculty of Science, Tokyo Kyoiku University, Bunkyo-ku, Tokyo 112
² Department of Biology, Kochi University, Asakura, Kochi 780, Japan

The life history of Symplegma reptans was studied by repeated observations on particular living animals and by observations on sectioned materials.

The oozooid produces its first bud about 10 days (17° -20° C) after metamorphosis, and produces a series of 4-7 buds by the time the oozooid begins to degenerate. The degeneration occurs about 30 days after metamorphosis. No gonad is formed in the oozooid even at the time when gonads are seen in the blastozooids of the same colony. Of the 7-9 protostigmata present in the newly metamorphosed oozooid, the anterior 3-4 are subdivided by the time of degeneration, but the posterior 3-5 remain undivided throughout the life of the oozooid.

A blastozooid makes its own first bud 3-4 days (17° -20° C) after its first appearance, when it is still scarcely more than "bud" itself. The growing blastozooid makes a succession of 3-6 buds at intervals of 2-4 days. Bud formation by a blastozooid come to an end about the time its gonad become macroscopically visible. Blastozooids live for 60 days or more, but at least some of them degenerate before the death or degeneration of the colony.

Microscopical sections suggest that the germ cells are formed directly from lymphocytes.