Immersion of cysts of Heterodera rostochiensis in potato-root diffusate results in larval emergence which may occupy up to two or three months. In a previous paper (Fenwick, 1950), the author dealt with the form of the hatching curve, and showed that any given curve was controlled by three parameters; the number of larvae finally emerging, the mean reaction time of the hatchable larvae and the standard deviation of that mean reaction time expressed in log-time units. Since it was also shown that each of these parameters was subject to considerable variation, it is obvious that maximum information and accuracy can only be obtained by continuing a hatching test until all larval emergence has ceased and plotting cumulative hatches at selected intervals of tune against log-time; in this way detailed information may be obtained regarding the parameters of the hatching curve.