In previous papers the migration of Ascaris lumbricoides in the rat and mouse has been traced to the point at which the larvae of the worm reach the trachea of these animals on the 8th day after infection. As the result of further experiments it is now possible to trace the migration through a further stage, namely that occurring from the 9th to the 15th days after infection. My experiments have not as yet been carried beyond the 15th day and in the following summary the statement that larvae occur in a given situation up to the 15th day is not intended to imply that they do not persist therein after that date.

I. In the following three experiments it will be shown that ripe eggs of Ascaris suilla can hatch in the intestine of the pig, that the larvae issuing from these eggs enter the body of the pig and pursue the same course through the body as in the rat and mouse. They have been found in the lung of the pig from the 6th to the 8th day and in the trachea on the 8th day. Dead larvae have been found in the faeces of the pig on the 11th day after infection (Expt. 6).

During the period 1913–16, I conducted a Survey of the Agricultural Zoology of the Aberystwyth Area, for which purpose the University authorities received a grant from the Board of Agriculture. The area thus examined comprised N. Cardiganshire and some adjacent borders of Montgomeryshire, roughly about 250 sq. miles. It falls into three main physical divisions:

I. The mountainous upland (or high plateau) of solid rocks frequently covered by a considerable depth of peat. The rock succession is only irregularly exposed in deep stream cuttings, while these valleys are occupied by boulder clay and river deposits.

II. The surface of the coastal plateau shows exposures of rock and of boulder clay. The clay is usually exposed and rarely covered with peat.

III. The fall line, which is intermediate. Here the boulder clay generally follows the valleys, and it is usually covered with a thin layer of peat. Much of this is readily cut through by small streams.

1. Certain flocks in the Aberystwyth Area having suffered considerably from Liver Rot, a Survey of the Agricultural Zoology was carried out between October, 1913, and October, 1916, special attention being given to the above disease and the bionomics of the host snail L. truncatula.

2. The Area comprised some 250 sq. miles of North Cardiganshire, etc., including Plynlymon, and falls into six natural divisions.

3. The presence of the disease has caused a number of local modifications in farm practice, designed to prevent, or mitigate losses. The disease was found to be on the wane within the Area, though endemic in certain places.

4. L. truncatula and L. peregra are the only abundant local species of the Genus. Considerable differences occur in the distribution of these two species. L. peregra was only studied in order to better understand the habits of L. truncatula. This latter species occurs in shallow water floored with Diatomaceous clayey mud, and is absent from soft mud, and peat. There is a marked coincidence between the distribution of clay and L. truncatula, and L. truncatula and Liver Rot.

5. The growth of the snails takes place throughout the year unless interrupted by drought or severe frost. Ova are deposited in March–April and hatch in May. The resulting snails, when they become adults, measure about 5 mm. in length. They in turn deposit ova during June–July. Drought usually limits further progress until the late Autumn, the snail being often very scarce during August–September.

6. Desiccation speedily kills L. truncatula. Local environmental conditions—rainfall, aspect, soil, vegetation, etc.—play a very important part in respect to its survival. Rainfall and its distribution through the year is the most important factor governing the increase, spread, and infectivity of the snail.

7. The ova masses dry rapidly and then resemble a hard inconspicuous scale. They resume their former size and shape when moisture returns, and many appear to be able to hatch subsequently, though the amount of desiccation they will withstand is not yet determined. In spite of prolonged droughts, L. truncatula re-appears, unless ditches, etc., have been cleaned out.

8. Roadside ditches are very frequently inhabited by infected snails and the drainage from them may be the cause of cases of rot.

9. Cercariae of D. hepaticum were obtained from L. truncatula in large numbers practically throughout the year; but not from snails measuring less than 4·5 mm. in length. Seventy cercariae were given off naturally, within 48 hours, from one specimen measuring 7 mm. in length. Heavily parasitized snails are adversely affected. A few cercariae, resembling those of D. hepaticum were obtained once from L. peregra.

In 1814 Rudolphi described, under the name of Amphistomum subtriquetrum, a fluke from the caecum of the European beaver (Castor fiber). Little of importance was added for many years; i.e., until 1897, when Otto described it somewhat fully including its internal anatomy, and 1901 and 1903, when Fischoeder wrote of it in his classical revision of the Amphistomidae. In 1914 Duff described a similar parasite, this time from the American beaver (Castor fiber canadensis) which she believes to be identical with that of the European animal.

It is well known that the eggs of the above-named mosquito remain viable when out of water for many months. Various workers, among whom may be named Theobald, Newstead, Francis and Mitchell, record varying periods up to nine months' duration.

Hyalomma monstrosum, Nuttall and Warburton, 1907 (Proc. Camb. Phil. Soc., Vol. XIV. pp. 392–416, figs. 41–45 of the ♂). The female is here described for the first time.

In 1909, Professor McIntosh of St Andrews University sent me a cyst from the abdominal cavity of a South African baboon, Cynocephalus porcarius Budd. The cyst, which was single, had been ruptured in removal, part of its contents had escaped, and some blood had entered it. The cyst measured about 20 mm. in diameter, was a typical hydatid, and resembled in its general structure the ordinary simple unilocular hydatid of man.

In 1911, I received from Dr Georgina Sweet of Melbourne University, two lots of Trematodes stated to have been collected respectively from the intestine of the tiger snake, Notechis scutatus, and the lungs of the copperhead snake, Denisonia superba. In 1916, Dr Burton Cleland, of the Bureau of Microbiology, Sydney, sent me two tubes containing similar parasites, obtained from the peritoneum of an unidentified snake killed on Flinders Island.

Nobody who studies the parasitic amoeba of the frog (Entamoeba ranarum) and the dysentery amoeba of man (E. histolytica) can fail to be struck by the remarkable resemblance between these organisms. The development of the former I described for the first time in 1908 and 1909, since when I have had exceptional opportunities of studying the latter; and I can state, with some confidence, that there is no constant structural character which will permit of a distinction being drawn between these two species. The active amoebae can usually be readily distinguished from one another by the inclusions (food bodies) in their protoplasm, but not by their own nuclear and cytoplasmic structure; but the precystic amoebae, devoid of all food bodies, and the cysts, at every stage in their development, are so closely alike that preparations of the one could be used as demonstration specimens of the other.