. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. NEURAL DIFFERENTIATION 15. Figure 8. Longitudinal section of a 24-h planula. Differentiating nematohlasts (single arrows) are visible in both the endoderm (E) and the ectoderm (EC). A young ganglionic cell (double arrows) is seen at the base of the ectoderm above the mesoglea (M). Its neurites are not yet fully formed. Triple arrows, endodermal interstitial cells. X250. Figure 9. Ectodermal ganglionic cell (arrow) in a 24 h planula. Note its spindle shape and extending neurites. X620. and ganglionic cells occupy the entire a
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. NEURAL DIFFERENTIATION 15. Figure 8. Longitudinal section of a 24-h planula. Differentiating nematohlasts (single arrows) are visible in both the endoderm (E) and the ectoderm (EC). A young ganglionic cell (double arrows) is seen at the base of the ectoderm above the mesoglea (M). Its neurites are not yet fully formed. Triple arrows, endodermal interstitial cells. X250. Figure 9. Ectodermal ganglionic cell (arrow) in a 24 h planula. Note its spindle shape and extending neurites. X620. and ganglionic cells occupy the entire anterior-posterior axis of the planula, whereas, nematoblasts and nemato- cytes are confined to the anterior and middle regions of the animal (Figs. 8, 9). In the ectoderm, ganglionic cells and nematoblasts are positioned in close proximity to the mesoglea, and interstitial cells are located slightly above these cells (, toward the outer ectodermal sur- face). In the endoderm, interstitial cells and nemato- blasts may be found in the central core or out closer to the mesoglea. As planulae mature (24-96 h) the numbers of ectodermal and endodermal interstitial cells, ectoder- mal and endodermal nematoblasts, ectodermal nemato- cytes, and ectodermal ganglionic cells increase. At 24 h, the nervous system begins to form (Martin, 1988a, b). This neural system is entirely ectodermal and consists of ganglionic cells (interstitial cell derivatives) and sensory cells (epithelial derivatives). Ganglionic cells form a neural plexus composed of cell bodies and their neurites; this plexus extends the entire length of the plan- ula and is located just above the mesoglea (Fig. 9). These ganglionic cells have originated from interstitial cells that have migrated from the endoderm to the base of the ecto- derm. Once in this ectodermal position, they elaborated morphological features characteristic of ganglionic cell differentiation. Interstitial cells traversing the ganglionic pathway in the
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
