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.

Observations on the Development of the Ventral Hypodermis

J.G. White, M. Anness, J.N. Thomson

Figure 1

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.

Figure 1