Fifteen children aged from 6 to 12 years who were infected with Ascaris lumbricoides were selected for the study. The number of eggs/g (e.p.g.) of stool was determined using Beaver's direct smear technique, Stoll's dilution egg count technique and Katz's modified thick smear technique. Beaver's direct smear method consistently gave a higher e.p.g. than the other two methods. Results of this study show that Katz's modified thick smear technique was the best of the three methods used. The e.p.g. depends on several factors: the amount of stool passed daily, the concentration of eggs within a stool sample, the daily egg output, the worm load, the age of the worm and the technique used for determining the egg load. The daily average egg output/female A. lumbricoides was estimated to be 238722 (range 134462–358 750) with an average e.p.g. of 3540. The estimation of worm load based on egg count is useful in determining the intensity of infection in an individual. The male/female worm ratio was estimated to be 1: 1·4.

Infections with either 300 infective Trichinella spiralis larvae or 400 embryonated eggs of Trichuris muris were effective in eliciting accelerated expulsion of heterologous challenge infections given 20 days after the primary infection. Accelerated expulsion could also be achieved by the administration of soluble crude worm antigen given 12 days prior to heterologous challenge or by adoptive transfer of mesenteric lymph node cells taken from mice infected with the heterologous parasite. Each species is capable of eliciting an accelerated secondary expulsion response in hosts that have been actively or adoptively immunized against the other species and these results are taken to indicate that there is a specific cross-immunity between T. spiralis and T. muris due to shared antigens. It is postulated that these shared antigens are derived from stichocyte granules.

‘Each organism must be examined as a biochemical entity before any reasonable understanding of helminth metabolism can be attained’ (Saz, 1969).

Preparations of isolated brush border plasma membrane of Hymenolepis diminuta and H. microstoma possess the following enzymatic activities: alkaline phosphohydrolase (E.C. 3.1.3.1); Type I phosphodiesterase (E.C. 3.1.4.1); ribonuclease (E.C. 3.1.4.22); adenosine triphosphatase (E.C. 3.6.1.3); and 5′-nucleotidase (E.C. 3.1.3.5). The following enzymatic activities could not be demonstrated in either membrane preparation: Type II phosphodiesterase (E.C. 3.1.4.18); cyclic adenosine-3′, 5′-monophosphate phosphodiesterase (E.C. 3.1.4.17); leucine aminopeptidase (E.C. 3.4.11.1); maltase (α-glucosidase; E.C. 3.2.1.20); and lactase (β-galactosidase; E.C. 3.2.1.23). These data generally agree with those of previous studies in which similar membrane-bound enzymes were demonstrated in intact (living) worms.

Caryophyllids are widely distributed cestodes of the fresh water siluriform and cypriniform fishes of the world. There are about 126 species and 45 genera and they constitute approximately 25% of the cestode fauna of fresh water fish (Mackiewicz, 1972). Benthic-feeding fish become infected by eating tubificid worms (Annelida; Oligochaeta) that harbour the cercomer-beariug, infective stage; the tubificids, in turn, are infected by eating the operculated eggs in mud. Such a brief synopsis belies the fact that these well-known tapeworms are at the very heart of important questions concerning the evolution of Cestoidea. One has but to read Bazitov (1976), Freeman (1973), Kulakovskaya & Demshin (1978), Mameav (1975), Malmberg (1974) and Mackiewicz (1981) to appreciate that great differences still exist as to how caryophyllids evolved and what role they may have played in the evolution of the more numerous strobilate tapeworms.