The normal ultrastructure of the fundic gastric glands of cattle is described and compared with those from calves infected with T. axei. Loss and alterations in structure of zymogen and parietal cells are observed and are related to changes observed by light microscopy. The significance of these changes is discussed.

The normal ultrastructure of the abomasal fundic glands in sheep is described and compared with those of sheep infected experimentally with T. axei. Alterations were observed in mucous, mucous neck and zymogen cells and the results are compared with a similar study in normal and infected calves.

It is concluded that Bearup's cercaria, described from Pyrazus australis in Australia, is different from Cercaria variglandis; the former develops into Austrobilharzia terrigalensis and the latter into A. variglandis (Syn. M. Chapini Price, 1929; M. variglandis Stunkard and Hinchliffe, 1952).

Bearup's cercaria should be henceforth treated as that of A. terrigalensis and not as C. variglandis.

(1) The structure of the microfilaria of Brugia (B. patei and B. pahangi) is redescribed and the development of B. patei is followed in the mosquito Aedes togoi for the first 4 days, up to the moult to the second larval stage.

(2) The buccal cavity, the pharynx (or oesophagus), and the pharyngo-intestinal valve of the second stage larva are formed around the pharyngeal thread of the microfilaria. Part of this thread is moulted with the microfilarial cuticle at the moult to the second larval stage.

(3) The intestine of the second stage larva is built up around the Innenkörper of the microfilaria from cells of the nuclear column.

(4) The R cells (G 2—G 4 cells) of the microfilaria and the anal vesicle of the microfilaria continue into the second stage larva and eventually the rectum is formed between them.

(5) The G cell (G 1 cell) does not form part of the gut of the second stage larva but becomes incorporated into the body wall with other cells from the nuclear column.

(6) The subcuticular cells of the microfilaria continue as elongate spindle shaped cells in the cords of the second stage larva.

(7) The significance of these results, which are at variance with earlier descriptions, are discussed and it is concluded that the microfilaria of Brugia is a very much modified first stage nematode larva, adapted to life in the capillaries of the vertebrate host. The microfilaria begins the metamorphosis to the structure of the second larval stage soon after entry into the insect vector.

Eight species of digenetic trematodes, 3 of them new, are reported in fishes from Sierra Leone. Stephanostomum africanum n.sp. (Acanthocolpidae) is from Pseudotolithus senegalensis, S.sierraleonensis n.sp. from Galeoides decadactylus, Pycnadena africana n.sp. (Opistholebetidae) from Lutjanus modestus, Megasolena hysterospina (Manter, 1931) Overstreet, 1969 (Haploporidae) from Chaetodipterus lippei, Aephnidiogenes senegalensis Dollfus, and Capron 1958 (Lepocreadiidae) from Pomadasys jubelini, Lepocreadioides cynoglossi Fischthal and Thomas, 1970, (Lepocreadiidae) from Cynoglossus senegalensis, Lasiotocus cynoglossi Thomas, 1959 (Monorchiidae) from Cynoglossus senegalensis, and Poracanthium ghanensis Fischthal and Thomas, 1970 (Opecoelidae) from Galeoides decadactylus.

By clarifying which taxonomic characters are of specific significance and by defining the intra specific limits of individual morphological variations, seventeen species of the genus Anisakis were shown to represent only three distinguishable forms, these being Anisakis simplex (Rudoiphi, 1809 det. Krabbe, 1878), A. typica (Diesing, 1860) and A. physeteris Baylis, 1923. The morphological characters in order of importance for identifying these species are the spicules, the postanal papillae, the form of the ventriculus, the position of the vulva and the form of the lips. These three species were also found to be satisfactory when discussed in geographical and ecological terms.

The four remaining species in the genus, Anisakis dussumierii (van Beneden, 1870), A. alexandri Hsü and Hoeppli, 1933, A. insignis (Diesing, 1851) and A. schupakovi Mozgovoi, 1915 are retained as species inquirendae for lack of sufficient information concerning them.

Five new species are described and nine known species and one new combination are reported from new hosts and new localities. The new species are: Prosogonotrema pritchardae, Uroproctinella attenuata, Bivesiculoides scari, Stephanostomum attenuatum and S. adinterruptum. The known species are: Genolopa trifolifer Nicoll, 1915, Anaporrhutum albidum Brandes in Ofenheim, 1900, Hymenocotta mulli Manter, 1961, Pleorchis sciaenae Yamaguti, 1938, Mehratrema dollfusi Srivastava, 1939, Buckleytrema indica Gupta, 1956, Acanthocolpus tenuis Manter, 1963, A. liodorus Lühe, 1906, and A. luhei Srivastava, 1939. The new combination is Alloheterolebes indicus (Gupta, 1968).

S. maltheei females could mature and produce eggs in the absence of males in mice and hamsters but only nonviable eggs were produced during the 88 week observation period. S. mansoni, S. rodhaini and S. bovis females were studied under similar conditions for up to 30, 36 and 66 weeks, respectively, but in none of these species were any eggs produced by the female worms. The contrasting behaviour of S. mattheei and S. bovis is further evidence of their specific distinctness.