The use of worm egg counts for observational and experimental purposes in naturally infested sheep has become very popular since Whitlock and Gordon (1989) introduced the simple and efficient McMaster slide technique. When using a dilution technique such as this, the accuracy of the count increases as more eggs are counted. In order to count more eggs when using the McMaster slide it is usually more convenient, in practice, to take more samples (i.e. count more cells) than to alter the dilution. It is therefore desirable to know the optimum number of samples which should be counted for each sheep when comparing the counts of naturally infested sheep. The usefulness of sampling on one or more days is another problem concerning experiments of this nature.

A comparative study has been made of the Pseudophyllidean cestodes harboured by Pinnipeds, mainly from the Northern Hemisphere. Thirty species of this group of cestodes have been recorded in the literature, and as a result of the present study these may be divided into the following:

Valid species: Diphyllobothrium cordatum (Leuckart, 1868); D. elegans (Krabbe, 1865); D. glaciale (Cholodkovsky, 1915); D. hians (Diesing, 1850); D. lanceolatum (Krabbe, 1865); D. scoticum (Rennie & Reid, 1912); Diplogonoporus tetrapterus (v. Siebold, 1848); D. fasciatus (Krabbe, 1865); and Pyramicocephalus phocarum (Fabricius, 1780).