Structure and function in the nematode pharynx

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Abstract
The simple cylindroid pharynx ofAscaris lumbricoideshas been shown to be characterized by a pharyngo-intestinal valve which is composed of two sets of valves. This is the only valve structure in the pharynx of this nematode. The pharynges ofOxyuris equi, Aplectana brevicaudataandPanagrellus silusiaehave a series of valve structures along the lengths of the organs. All these types have a valve at the anterior end of the corpus, corrugated ‘valves’ in the posterior bulb, and pharyngo-intestinal valves. A valve between the corpus and the isthmus has been shown inOxyuris.In all the nematodes studied the pharyngo-intestinal valve is characterized by an overlapping of the muscle fibres associated with the valve and the main musculature of the pharynx that immediately precedes them. It has been suggested that the pharyngo-intestinal valves of the types studied may have evolved from the type of valve found in the Enoplina.The marginal tissues of the pharynx ofAscaris lumbricoideshave been shown to be composed of three types of tissues. It has been suggested that the marginal tissues have a suspensory and skeletal function. The suspensory strands subserve the first function, while the investing strands and the associated fibrous layer provide a longitudinal skeletal structure in the pharynx. InOxyurisno fibrous layer is associated with the marginal tissues.I would like to thank Professor J. E. Harris and Dr H. D. Crofton for their help and criticism during the course of this work, which was carried out during the tenure of a Postgraduate Studentship awarded by the Agricultural Research Council.