The trematodes described below were collected at the Marine Biological Station at Ghardaga, Red Sea.

Type specimens are deposited in the Department of Parasitology of Faculty of Medicine, Abbassia, Egypt.

All measurements are in millimetres.

Suckling rats of various ages were infected with large doses of the 'RH' strain of Toxoplasma gondii either by intraperitoneal injection or by feeding. Among the intraperitoneally infected rats of different age-groups, the percentage of survival remained low up to 23-day-old rats, after which it increased sharply. The percentage of infection was 100%. Among the rats infected by feeding, the percentage of survival was low in rats up to 5 days old at the time of feeding, after which it increased sharply and remained more or less constant. The percentage of infection decreased gradually with increasing age. These results are discussed in the light of previous knowledge.

My thanks are due to Professor P. C. C. Garnham for his interest in this study and for providing me with the facilities. My thanks are also due to Mr Z. W. Pokrzywnicki of the Department of Bacteriology for his assistance with the Polish literature.

Studies on the susceptibility of the guinea-pig to infection with Schistosoma spindale Montgomery are reported.

Of twenty-two guinea-pigs, examined 33–153 days after exposures to 8000–50,000 cercariae of S. spindale, seventeen furnished conclusive evidence of the development of the female schistosome and two furnished inconclusive evidence. The male S. spindale developed in all the animals.

The female schistosomes attained maturity in 48 days or more and laid viable ova which could be detected in the liver, intestinal wall and lungs, but not in faeces.

The pathological lesions caused by the parasite consisted of thrombosis in the liver and lungs due to adult worms and pseudotubercles in the liver and nodules in the intestinal wall due to the eggs.

The guinea-pig shows varying degrees of individual susceptibility to infection with S. spindale and is an unsuitable host for the parasite, more especially for the female schistosome.

During an investigation into the tick fauna of Africa, Dr H. Hoogstraal sent me a specimen of a female Ixodes tick collected from Angola, which was deposited in the Chicago Natural History Museum. This is a new species which I describe below under the name of I. heinrichi.

The identity of Hyalomma lusitanicum K. and H. anatolicum K. is discussed. The male and female of the two species are described. H. anatolicum is considered as species inquirenda, but distinct from H. anatolicum anatolicum (sensu Pomeranzev) and H. anatolicum excavatum (sensu Pomeranzev). H. anatolicum anatolicum and H. anatolicum excavatum are considered to be one polymorphic species. This species should be called H. excavatum as it tallies with the still existing type specimen of H. excavatum Koch; it should not be called H. anatolicum as it does not correspond to Koch's description of H. anatolicum. The name H. anatolicum should for the present be reserved for a species resembling H. excavatum, but characterized by the light yellow colour of the anterior part of the scutum. It remains to be determined by breeding experiments whether this character is constant.

A description is given of the following three new trypanosomes from freshwater fishes: (1) Trypanosoma winchesiense sp.nov. of Mirror carp, Cyprinus carpio (variety), obtained in Essex, England; (2) T. batrachi sp.nov. of Clarias batrachus from India, and (3) T. danilewskyi var.nov. saccobranchi of Saccobranchus fossilis from India.

Among the earlier investigators, attempts to cultivate trypanosomes in NNN medium were made by Petrie (1905) and Brumpt (1906a), who isolated Trypanosoma denilewskyi and T. granulosum, respectively, but failed to estabilsh them in subculture.

1. Annual fluctuations in the percentage of L. saxatilis infected by Cercaria ubiquitoides at Whitstable, Kent, are described.

2. Females are consistently more frequently parasitized than males.

3. At higher shore stations more L. saxatilis are parasitized than at lower shore stations.

4. Possible reasons for the above phenomena are discussed together with the relationship between trematode infection and the reproductive activity of L. saxatilis.

1. The distribution of non-specific esterase and of cholinesterase in Ascaris lumbricoides has been determined using histochemical methods.

2. Non-specific esterase has been shown to be present in the cuticle, in the walls of the excretory canals, in the innervation processes of the muscles, in the coelomocytes, in the oesophageal glands, in the intestine, in the rectal glands, in the male and female reproductive systems, in parts of the nervous system and as 'caps' of enzyme on fat globules in the hypodermis and muscles.

3. Cholinesterase has been detected in the innervation processes and sheath of the muscles, in the sphincter muscles, in the intestine, in the sensory papillae and amphids, and in parts of the nervous system, including a nerve in the spicules.

4. Parts of the nervous system and the innervation processes of the muscles contain an esterase which is not inhibited by cholinesterase inhibitors and it is suggested that there may be esterase, distinct from cholinesterase, involved in nerve transmission.

5. Merocrine secretion of esterase has been observed in the intestine.