1. The suckling 10-day-old mouse harboured fewer worms than the weanling 15-day-old mouse after both 5 and 10 days' infection.

2. The adult male mouse, however, harboured significantly more worms when fed on milk than when fed on rat cake after both 5 and 10 days' infection.

3. These results were discussed in relation to the effects of diet and gut length on the susceptibility of the host.

This work was done during the tenure of a Department of Scientific and Industrial Research Studentship. My thanks are due to Dr E. T. B. Francis for his helpful and critical supervision, and to Professor I. Chester Jones, in whose department the work was done, for the facilities he provided.

A new species, Demodex aurati, is described from the Golden Hamster, Mesocricetus auratus. It differs in both morphological detail and ecological niche from D. criceti present on the same host.

When pieces of heavily parasitized skin were ‘subplanted’ for 100 days no change in morphological features of either D. aurati or D. criceti occurred.

D. aurati is a low grade pathogen, apparently only harvesting the cells of the follicular epithelium.

The life cycle of D. aurati is described.

The presence on one host species of two different species of this genus, which has affinities with demodicids of evolutionally remotely related hosts, poses an interesting problem in species specificity and ectoparasite evolution.

I wish to thank Dr Miriam Shaw, Miss Shirley DiBenedetto and Miss Helen Krause for their excellent technical help, and Dr Lawrence Bartlett and Dr Harold Rauch for perusal of the manuscript and suggestions on project procedure.

This investigation was supported by a research grant E-562 from the Institute of Allergy and Infectious Disease, of the National Institutes of Health, Public Health Service.

The three species of gregarines described in the present paper—Monocystis cambrensis sp.nov., M. lanceata sp.nov. and M. elongata (Phillips & Mackinnon, 1946), Loubatières, 1949—are all parasites of British earthworms. The observations upon which these descriptions are based form part of a larger survey of the monocystid fauna of several British earthworms. The methods used are fully described in a previous paper (Rees, 196).

Three new species of cestodes are described. They are: Joyeuxiella paucitestis sp.nov. from the Rusty Spotted Genet, Genetta rubiginosa; Diplopylidium paurodex sp.nov. from the Rusty Spotted Genet, Genetta rubiginosa; Taenia crocutae sp.nov. from the Spotted Hyaena, Crocuta crocuta.

Re-descriptions are given of Joyeuxiella fuhrmanni (Baer, 1924), Fuhrmann, 1935, and Taenia ingwei Ortlepp, 1938, with particular reference to differences between the original descriptions and those based upon the present material.

Five species of Glossina (G. morsitans, G. pallidipes, G. austeni, G. brevipalpis and G. palpalis) have ovaries containing two polytrophic ovarioles, each of which contains a single egg follicle. In all these species the right ovary is more highly developed than the left at emergence. This type of ovary is probably common to all species of Glossina.

The development of the egg follicles in G. morsitans pupae is described. It is shown that the cycle of development whereby eggs are produced alternately from right and left ovaries is established during pupal development and that some yolk deposition has occurred in follicle A (right ovary) and follicle C (left ovary) before the fly emerges from the puparium.

In G. morsitans, it is shown that the size of the egg follicles in newly emerged flies is correlated with the size (R.D.W.) of the fly, larger females having more yolk laid down in their follicles before emergence. This is probably correlated with the state of reserves in the fat body. It is also shown that there is a seasonal variation in follicle size in newly emerged flies, this variation is probably correlated with variations in temperature acting upon wild females during pregnancy and upon the pupae, as temperature is known to affect both size and fat content of wild tsetse flies.