STUDIES ON REPRODUCTION IN THE COMPOUND ASCIDIAN, SYMPLEGMA REPTANS: RELATIONSHIP BETWEEN NEURAL COMPLEX AND REPRODUCTION

¹ Zoological Institute, Faculty of Science. Tokyo Kyoiku University, Otsuka, Tokyo, Japan

1. The neural complex was examined for induction of sexuality in a compound ascidian, Symplegnia reptans. The number of Gomori-positive neurosecretory cells in the neural ganglion increases rapidly while oocyte development proceeds from previtellogenesis to vitellogenesis and is constant in sexually mature zooids. However, such cells decrease in number in conditions disadvantageous for gonad development. The decrease in cell numbers in isolated aged zooids may result from lysosomal digestion of granules.

2. Fully grown ova and previtellogenic oocytes suffer mild influences from ganglion ablation. However, vitellogenic oocytes always suffer profound damage from the operation.

3. In sexually mature zooids, electrical stimulation to the neural ganglion leads to decrease in the number of Gomori-positive neurosecretory cells. The stimulation accelerates growth of previtellogenic oocytes, but does not affect oocytes in other developmental stages.

4. These findings suggest that the ganglionic neuroscretory cells in Symplegma may function in sexual reproduction, especially in the vitellogenesis.