The ultrastructure of the sensory cells in the chemoreceptor of the ommatophore of Helix pomatia L.

Summary

Most of the sensory cells found in the chemoreceptor of the ommatophore of Helix pomatia are typical bipolar cells. The chemoreceptor is divided by a furrow into two parts; within the ventral subdivision the layer of sensory cell bodies is thicker than in the dorsal part. According to the differentiations of the apical surface of the dendrites, it is possible to distinguish six different classes: a) dendrites with one cilium and 75 nm thick cytofila (sometimes dendrites of identical appearance possess more than one cilium); b) dendrites with several cilia and 150 nm thick cytofila; c) dendrites with several cilia, 50 nm thick cytofila, and long, striated rootlets; d) dendrites with several cilia but without cytofila; e) dendriteg with 130 nm thick cytofila but without cilia; and f) dendrites with 65 nm thick cytofila but without cilia; dendrites of this class are the only ones with a cytoplasm more electron dense than that of the surrounding supporting cells. All these dendrites are connected to the surrounding supporting cells by terminal bars, each consisting of zonula adhaerens, zonula intermedia and zonula septata.

The perikarya of the sensory cells measure approximately 15 μm by 8 μm and enclose 10 μm by 6 μm large nuclei. Axons, originating from these perikarya, extend to the branches of the digital ganglion. In the distal part of this ganglion the axons come into synaptic contact with interneurons, but in our electron micrographs it was not possible to coordinate processes and synapses with the corresponding neurons.