Pumping of the pharynx of Panagrellus has been shown to be a complex process involving three stages: the uptake of a number of globules by the corpus, the passage of the aggregate globule through the isthmus, and expulsion of the globule into the intestine by a number of pumps of the posterior bulb. It is suggested that Aplectana pumps in a similar manner to Panagrellus but at a faster rate. The pharynx of Rhabditis operated in two stages, involving the uptake of food first by the anterior half of the organ, and the subsequent passage of the ingested material through the isthmus and posterior bulb.

The pumping action of the posterior bulb suggests that the corrugated valves have a primarily valvular function. Regurgitation of intestinal contents through the pharynx is prevented by the internal pressure of the animals tending to force the walls of the organ together, and by the action of series of valves found throughout the lengths of the pharynges.

I should like to thank Professor J. E. Harris and Dr H. D. Crofton for their help during the course of this work, which was carried out during the tenure of a Postgraduate Studentship awarded by the Agricultural Research Council.