Two age groups of parasite-free lambs, 4 months and 8 months, were infected with 50 000 infective larvae (L3) of T. vitrinus. A further group of 8 month old lambs were infected with 250 000 L3 T. vitrinus. The lambs were slaughtered at intervals after infection, and the size and linear distribution of their intestinal worm burdens examined and compared statistically. After the 50 000 L3 infections, it was found that a higher percentage of the initial inoculum had become established in the younger lambs but that there were no differences between the intestinal distributions of the population in either age group.

After infection with 250 000 L3, the percentage of the larvae retained changed with time. Up to sixteen days post infection, 38% of the larvae administered were retained; thereafter the percentage fell to 22%. The linear distribution of the population in this size of infection showed that a significantly greater percentage was present between 4.8 and 7.2 metres distal to the pylorus when compared with that after infection with 50 000 L3.

Effective treatment of mice with six to eight week-old patent S. mansoni infections with any one of five schistosomicidal agents (Oxamniquine, Praziquantel, potassium antimony tartrate, Niridazole and Hycanthone) resulted in a reduction in the degree of resistance to homologous challenge in the treated animals when compared with the level of resistance to reinfection observed in untreated mice with intact primary infections. Mice challenged five to six weeks after treatment with Praziquantel, Niridazole or Hycanthone demonstrated a lower level of resistance than mice challenged within 10 days of the termination of the chemotherapeutic schedules. Direct comparison of Praziquantel with potassium antimony tartrate indicated that treatment with the former drug allowed retention of a greater level of acquired resistance than the antimonial in the immediate post-treatment period. Resistance to reinfection in Hycanthone-treated mice was not restored by intravenous injection of S. mansoni eggs before challenge.

Phaneropsolus mulkiti sp. n. is described from the sand lizard Liolepis belliana Gray, 1827 from Bukit China, West Malaysia. Morphologically it is separate from all reported species of the genus Phaneropsolus Looss, 1899 and is the second species reported from a poikilothermic host.

Neocamallanus bareilliensis n. sp. has been described from the intestine of a freshwater fish Channa punctatus from Bareilly (U. P.) India. It has been distinguished from the other three species of the genus reported so far.

Proteocephalus pentastoma and Polyonchobothrium polypteri are redescribed from specimens from Polypterus spp. in the Sudan. Proteocephalus pentastoma is considered to be a valid species.

Bufonerakis andersoni n. gen. n. sp. from Bufo arenarum of Argentina is described. Bufonerakis is proposed for species in the Subfamily Meteterakinae with a short muscular vagina and opposed uteri. The other genera in the subfamily, Meteterakis Karve, 1930, and Gireterakis Lane, 1917, have an elongate vagina divided into a short muscular portion and long common uterine trunk giving rise to two parallel uteri in the posterior third of the worm. Meteterakis rodriguesi Vicente and Corrêa Gomes, 1971, is reclassified as Bufonerakis rodriguesi n. comb.

Ascaridoid nematodes reported from terrestrial and freshwater chelonians are described under two monotypic genera, Angusticaecum and a new genus Krefftascaris respectively. The former genus contain A. holopterum (Rodolphi, 1819) Baylis, 1920 [synonym A. brevispiculum Chapin, 1924], reported in the natural state from testudinid and emydid tortoises in Europe, U.S.S.R., Iran, Brazil and North Africa. Teh latter genus contains a new species, K. parmenteri, reported from chelid freshwater turtles in Eastern Australia. It is concluded that the former is most closely related to species in other genera in terrestrial reptiles, whereas the latter is closest to Gedoelstascaris spp. in crocodilians. Host-parasite relationships over evolutionary time between ascaridoids and chelonians are discussed.