Simplified representative drawings of DL and VL cephalic sensilla are seen in GliaFIG25a, b, and GliaFIG26. Note, for reasons of simplicity, only left side socket and left side CEP neurons are shown in GliaFIG25a. Also, axons of CEPDL, CEPVL, CEMDL and CEMVL as well as processes of the right side sheath cells are omitted. Projections from the sheath cell somata around the nerve ring (NR) are grossly simplified here as a cylindrical ring (compare figures below). Sheath cell nuclei are indicated as gray spheres for the left side pair. Socket cell processes terminate in enlarged doughnut-shaped rings to connect the the sheath pocket to the inner cuticle (GliaFIG25b). TEM's of cephalic endings can be seen in Ward et al, 1975 (Figs 8-13) and Ware et al, 1975 (Figs 6-7). CEP neurons are suggested to be mechanosensory, whereas CEM neurons which are only found in males, may function as chemosensory (Perkins et al., 1986).
4 CEPsh cells (CEPshVL, VR, DL, DR) form a thin, cylinder-like covering around the nerve ring separating the nerve ring from the hypodermis (GliaFIG25a-g). Their anteriorly directed processes travel with those of CEP neurons and CEPso cells (see GliaFIG25a-g and GliaFIG26 ). At the level of lips, CEPsh processes form a pocket around the CEP neuron dendrites (GliaFIG25b). Note that in GliaFIG26, CEP neuron axons that travel to the NR are not shown and CEPsh nuclei are indicated as dark ovals on the left side cells for reasons of simplicity. Narrow extensions from the sheath cells extend radially to interpose themselves at muscle-hypodermis boundaries. It has been suggested that CEPsh cells provide important substrates for early axon guidance in building the nerve ring (Wadsworth et al, 1996).
Cross section of CEPsh cells at the level of the nerve ring (NR) is shown in GliaFIG27 below. Note that thin CEPsh processes enter between hypodermis and muscle cells and separate NR neuropil from hypodermis and muscle.
Structure of CEPshVL, lateral view is shown below in GliaFIG28. To see TEM tracings of CEPshVL click on the section numbers: 1-2-3-4-5-6-7-8-9-10 on the image, or on the section thumbnails on the right. Nuclei of CEPVL and its sheath cell (indicated as gray oval) lie very close together. Note that extensions of the CEPshVL also wrap the ventral ganglion (VG) neuropil (Also see Fig. 16 in White et al, 1986)
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