. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SYMPLEGMA GANGLIA AND REPRODUCTION 227 tion, that is, zooid growth and bud formation. The same inhibitory influences of neurosecretory cells were shown in nemertines (Bierne, 1970) and in nereid polychaetes (Clark, 1965; Baskin and (folding, 1970). On the other hand, a positive function has been demonstrated in many other invertebrates, such as turbellarians (Grasso and Quaglia, 1971), molluscs (Geraerts and Algera, 1976; Wijdenes and Runham, 1976), non-nereid polychaetes (Howie, 1966; Gouedard- Couadou and Vicente, 1971), a
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SYMPLEGMA GANGLIA AND REPRODUCTION 227 tion, that is, zooid growth and bud formation. The same inhibitory influences of neurosecretory cells were shown in nemertines (Bierne, 1970) and in nereid polychaetes (Clark, 1965; Baskin and (folding, 1970). On the other hand, a positive function has been demonstrated in many other invertebrates, such as turbellarians (Grasso and Quaglia, 1971), molluscs (Geraerts and Algera, 1976; Wijdenes and Runham, 1976), non-nereid polychaetes (Howie, 1966; Gouedard- Couadou and Vicente, 1971), and arthropods (Tombes, 1970; Adiyodi and Adi- yodi, 1970 for reviews). In S\niplegma, the pattern of occurrence of Gomori-positive neurosecretory cells is different from that of Hydra. Active zooid growth and bud formation were observed in both young and aged zooids isolated from the central region of a colony, but they showed only a few such neurosecretory cells in their ganglia. As shown in Figure 3, variation in the number of Gomori-positive neurosecretory cells is superficially related to oocyte development. That is, the cell number increases rapidly when the oocyte proceeds from previtellogenesis to vitellogenesis. In addition, these cells decrease in number under conditions disadvantageous for gonad development. Thus, the neurosecretory cells in Symplegma seem to be functionally insignificant in asexual reproduction but to have some significance in sexual reproduction. If this is so, surgical removal of the ganglion should affect gonad development. The most distinctive effect of the operation was the break- down of oocytes in Stage 2, while young Stage 1 oocytes were mildly affected by the operation. Similar results have been obtained in Ciona (Bouchard-Madrelle, 1967). But studies in Chelyosoma showed that neural-complex ablation has no effect on gonad development (Hisaw ct al., 1966). Additional studies to com- pare single ascidians with compound ones or to compare spec
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
