Worm Breeder's Gazette 5(2): 43
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
In the course of our studies of the ventral nerve cord we have reconstructed the ventral hypodermis of several animals from electron- micrographs of serial sections. Although only a few developmental stages have been sampled some of the observations may be of general interest. 5 Hours Post-Hatch. At this stage the ventral hypodermis is cellular, the bulk of it being made up of the ventral cord precursor or 'P' cells. These are arranged as 6 pairs of bilaterally symmetrical cells with laterally situated nuclei. Each cell is joined to its symmetrical partner by a desmosome which is situated exactly on the ventral mid-line. The seam or 'V' cells are starting to divide at this time. The anterior regions of these cells send processes which run ventrally and meet at the ventral mid-line, thus separating pairs of P cells. It seems as if these regions start behaving like ventral syncytial hypodermal cells (the ultimate fate of the anterior daughter) before the divisions of the V cells are complete. [See figure 1] 18 Hours Post-Hatch. The seam cells have all completed their divisions and the cytoplasm of the syncytial anterior daughter cells has spread ventrally, undercutting that of the p cells laterally. The P cell nuclei and lateral cytoplasm are migrating into the ventral cord at this stage. The bilateral symmetry is lost at this point as the P cells arrange themselves as a single atero/posterior file. Left may end up either anterior or posterior to right although one configuration is usually favoured. 10 Hours Post-Hatch. The P cells start to divide, budding off an anterior daughter. The posterior part of the cell maintains its desmosome belt attachments to adjacent hypodermal cells throughout cleavage. The anterior part has no desmosomes and becomes a neuroblast when cleavage has completed. Subsequent Development. P1, P2 & P9-11 fuse with the hypodermal syncytium by the L1 moult. P3-P8 divide during mid-L3. If the somatic gonad is not present these cells will fuse with the hypodermal syncytium by the adult stage. In normal development P5-P7 will be induced to proliferate and produce a vulva, most of whose cells are unfused in the adult.