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The neural pathways for touch-induced movement in Caenorhabditis elegans contain six touch receptors, five pairs of interneurons, and 69 motor neurons. The synaptic relationships among these cells have been deduced from reconstructions from serial section electron micrographs, and the roles of the cells were assessed by examining the behavior of animals after selective killing of precursors of the cells by laser microsurgery. This analysis revealed that there are two pathways for touch-mediated movement for anterior touch (through the AVD and AVB interneurons) and a single pathway for posterior touch (via the PVC interneurons). The anterior touch circuitry changes in two ways as the animal matures. First, there is the formation of a neural network of touch cells as the three anterior touch cells become coupled by gap junctions. Second, there is the addition of the AVB pathway to the pre-existing AVD pathway. The touch cells also synapse onto many cells that are probably not involved in the generation of movement. Such synapses suggest that stimulation of these receptors may modify a number of behaviors.

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The biogenic amines serotonin and octopamine are present in the nematode Caenorhabditis elegans . Serotonin, detected histochemically in whole mounts, is localized in two pharyngeal neurons that appear to be neurosecretory. Octopamine, identified radioenzymatically in crude extracts, probably is also localized in a few neurons. Exogenous serotonin and octopamine elicit specific and opposite behavioral responses in Caenorhabditis elegans , suggesting that these compounds function physiologically as antagonists.

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Mutations in two nonessential genes specifically block the phagocytosis of cells programmed to die during development. With few exceptions, these cells still die, suggesting that, in nematodes, engulfment is not necessary for most programmed deaths. Instead, these deaths appear to occur by cell suicide.

Moulting of Caenorhabditis elegans has been observed by Nomarski interference contrast microscopy, and by electron microscopy of animals at selected stages. The wild type, cell division mutants and animals in which cells had been ablated by a laser microbeam were examined. The median lateral hypodermis, or "seam", is required for the formation of alae and for dauer larva maturation. During cuticle deposition, large Golgi bodies are seen in the seam cells. The excretory system is not essential for moulting.