It has been shown in an earlier paper that if the eggs of parasites are not deposited in unparasitised hosts alone, but distributed according to the laws of chance among unparasitised hosts and hosts already attacked by individuals of the same species, and if all the parasites develop successfully, no matter how many enter a single host, then the effect upon the time required for the extermination of the host, as compared to that which is required if only unparasitised hosts are chosen, is relatively slight.

The hypothesis examined in this paper is that when several parasites enter a single host, one, and only one, will develop successfully. It is shown that in such a case, provided the reproductive rate is decidedly greater than that of the host (e.g. 1·5 times as great), the effect on the time required for the extermination of the host by the parasite will be very little if at all greater than when superparasitism causes merely a loss in efficiency, as in the hypothesis previously examined. When the reproductive rate of the host is practically or actually equal to that of the parasite, the process of control will be seriously retarded, the delay being very much greater than in the preceding hypothesis. Control will, however, occur, even in this case.

Superparasitism of the type here examined will therefore not necessarily produce any marked retardation of the process of control in cases where control within reasonable time would otherwise be probable.