Structure and function in the nematode pharynx

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Abstract
The pharyngeal pump of Ascaris has been shown to have a very high capacity. While the contraction rate of the organ is probably of the same order as those of complex pharynges, the volume of material ingested at each pump is relatively higher. It is suggested that the pharynx acts as a simple two-stage pump in which half the lumen is filled with food at any one time.It has been suggested that the antagonism to the radial musculature of the pharynx resides in changes related to an increase in the diameter of the pharynx during the opening of its lumen. It is suggested that the closing of the lumen is facilitated by the increased tension in the outer coat of the pharynx and in the suspensory strands of the marginal tissues; and by the contraction of the radial musculature that is orientated towards the sides of the sectors of the pharynx, towards 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.