The observations here recorded relate to rat-fleas: (I) in Suffolk and North Essex, and (II) in Cambridgeshire.

To summarize our principal observations made in the course of the investigation into the rat-fleas of the suspected plague area of East Suffolk, July—October, 1911:

(1) We found an average of four fleas per rat: 822 rats were examined and 3293 fleas taken.

(2) The average was subject to a local variation (0·6 to 6·5).

(3) 15 species of fleas were taken from the rats, but of these there were only two species, C. fasciatus and C. agyrtes, which occurred in any numbers.

There were C. fasciatus 1986 or about 60 per cent.

C. agyrtes 1257 or about 38 per cent.

Rare species 50 or about 2 per cent.

(4) The average number of fleas per rat and the percentage of rats infested by fleas showed a well-marked seasonal variation, there being a considerable decline in the numbers as the cooler weather came on. Ceratophyllus fasciatus and Ctenophthalmus agyrtes both participated in a similar way in this variation.

(5) C. fasciatus is chiefly found on rats caught near human habitations; C. agyrtes on those caught in the hedgerows.

The following record relates to fleas collected from rats in and about Cambridge during the period 3rd March, 1909, to 20th November, 1911. We had difficulty in obtaining rats in Cambridge during the year 1911 owing largely to the high price asked by professional rat-catchers who usually sell them for sporting purposes. We have, consequently, included data collected by us during the two years before this investigation was undertaken on behalf of the Local Government Board.

The importance of the Argasidae, in relation to the transmission of disease, has suggested the need of a moderately detailed description of the anatomy of an example of the family. With the object of supplying this want, the authors have made a study of a widely distributed species—Argas persicus—and they venture to hope that the work embodied in the following pages will furnish something towards the much-needed information, the present lack of which adds to the many difficulties which are encountered in investigations concerning the life-stages of pathogenic Haematozoa.

The ornamentation so characteristic in Amblyomma, Aponomma, Dermacentor, and occasionally met with in species of Rhipicephalus and Hyalomma, is of use to the systematist in the differentiation of species. In many descriptions of ornate Ixodidae the colours are referred to as “metallic” owing to the sheen they possess when the ticks are preserved in alcohol.

In May 1912 when on the way with our Floating Laboratory to Rejaf, en route for the sleeping sickness district in what was formerly the Lado Enclave (now part of Mongalla Province), the late Colonel Mathias shot, near Renkwood station on the White Nile, two specimens of the Senegal or red-fronted gazelle—Gazella rufifrons. I found one of these animals, a female in good condition, heavily infected with sarcosporidiosis, the diaphragm, the intercosted muscles and those of the thigh being specially affected, though the striped muscle fibre everywhere contained cysts in varying numbers. In the light of the observations made by Probst and Francis (1910) the blood was carefully examined but no sarcosporidial spores were found in it nor were any blood parasites present.

When, in June 1911, I took over the charge of the Colony and Yaws Hospitals at St George's, Grenada, I learned from the Medical Reports that ankylostomiasis was existent in the Colony—a dozen cases having been treated in the Colony Hospital for this disease during the previous year, and one case having been met and treated in one of the out-districts.

Rhipicephalus appendiculatus requires three hosts upon which to feed in its larval, nymphal and adult stages. The larvae remain upon the host 3–7 days in most cases; when they remain considerably longer they either do not imbibe blood freely or they may not actually attach themselves on the day on which they were placed on the host; gorged larvae have dropped off the host up to 15 days after the unfed larvae were placed on the host. Nymphs remained upon the host 5–11 days and fertilized replete females abandoned the host after 6–14 days. The males may stay on longer. Unfertilized females may remain upon the host up to 24 days. The temperature at which the host is maintained, within the limits observed, exerts no apparent influence upon the time that the different stages of the tick remain attached. Metamorphosis takes place: from egg to larva in 32–65 days at 17–19° C.; from larva to nymph in 4–6 days at 30° C., in 21–41 days at 15–17° C., in 60–75 days at 13–14° C.; from nymph to adult in 10 days at 37° C., in 21–28 days at 20° C., in 64 days at 14° C. Temperature therefore markedly influences the rate of development. Oviposition commences 6–23 days at 17–19° C. to 50–61 days at 12° C. after the female abandons the host, the process lasting 15–56 days, during which period the female lays 3000–5770 eggs. Unfed larvae and nymphs were still lively after 333 days and 164 days respectively in a tightly corked bottle maintained at room temperature in a darkened cupboard in the laboratory. Unfed adults were lively after 181 days on moistened earth in a gauze covered jar kept in the cupboard; we have one lot of which a few individuals were living (unfed) after 630 days, a single male being still alive after 682 days (21. iii. 13).