1. The family Diclidophoridae Fuhrmann, 1928 has been revised, and the diagnosis of the replacing family Choricotylidae has been given.

2. Keys to the genera and species of the Choricotylidae have been constructed.

3. All species of the family have been reviewed and a diagnosis of each has been given.

4. Species previously referred to the genus Diclidophora have been transferred to the genus Choricotyle.

5. The following taxonomic changes have been proposed:

(a) Choricotyle merlangi (MacCallum, 1917) as a nom. nov. for the ‘Diclidophora merlangi Kuhn, 1829’ described by MacCallum (1917).

(b) Choricotyle charcoti (Dollfus, 1922 a, b) as a n.comb. to replace Cyclo-bothrium charcoti Dollfus, 1922.

(c) Diclidophora ‘species’ Fuhrmann, 1928 as a synonym of Choricotyle charcoti (Dollfus, 1922a, b).

An account is given of ultrafiltration studies with 9 plant viruses. It is shown that 3 of these viruses filter in a consistent manner and appear to have approximately spherical particles. These three are Lycopersicum virus 4 (tomato bushy stunt virus), Nicotiana virus 11 (tobacco necrosis virus) and Nicotiana virus 12 (tobacco ringspot virus). The filtration end-point of 40 mμ is the same in each case and from this a particle diameter of 13–20 mμ is calculated. There is a peculiarity, however, in the filtration curve of tobacco necrosis virus which shows itself in a “bench” or “shelf” and which suggests either a polydisperse system or some degree of dissymmetry of particle shape.

Great difficulty was experienced in filtering Nicotiana virus 1 (tobacco mosaic virus) and its strains. A value of 13–20 mμ was obtained for the particle diameter of the type virus and this agrees well with measurements obtained by other methods. The filtration results, however, suggest that the infective units are not of the same length and that this variability may be considerable. Similar difficulty was experienced in filtering Solanum virus 1 (potato virus X), another rod-shaped virus; the end-point was found to be 100 mμ, from which a particle diameter of 33–50 mμ is calculated. It was not possible to obtain a definite filtration end-point for Cucumis virus 1 (cucumber mosaic virus), probably because of the low initial concentration of virus in the extracted sap.

While making a survey of the parasites of littoral fishes at Cullercoats, Northumberland, parasites from Mola mola and Raniceps raninus came into my possession. These fishes are rarely found in British waters and so far no parasites have been recorded from R. raninus in British waters.

Extracts of caterpillars and other insects are shown to inhibit the infective power of tobacco mosaic and tobacco necrosis viruses. The inhibitor is not sedimented after spinning for 2½ hr. at 30,000 r.p.m. Experiments with non-vector insects such as caterpillars have shown that the virus of sugar-beet curly-top, of tobacco ringspot and other viruses, are destroyed within the body of the insect. On the other hand, tobacco mosaic virus passes through the body of the caterpillar unchanged though greatly reduced in concentration. By the use of the specific insect vector and artificial feeding methods it was possible to recover the virus of curly-top 24 hr. after it had been injected into the blood of the caterpillar but the viruses of tobacco mosaic and tobacco necrosis could not be so recovered. Experimental evidence is given to show that the virus of beet curly-top is present in the saliva of viruliferous insects.

Specimens of Plectanocotyle gurnardi were obtained by the writer from the gills of Trigla cuculus L. and T. gurnardus L. during trawling operations at the Irish Atlantic Slope fishing grounds in August 1938 and July 1939. One specimen of Plectanocotyle gurnardi was collected from a Trigla gurnardus and seven specimens of the same parasite from eight specimens of T. cuculus, the greatest degree of infestation encountered being 3 parasites per host fish. Plectanocotyle gurnardi has been recorded previously, under one or other of the synonyms listed above, from Trigla gurnardus by van Beneden & Hesse (1863), T. Scott (1901, 1905), A. Scott (1904), Lebour (1908), and Little (1929); from T. lucerna L. by A. Scott & Little; and from Trigla ‘sp.’ by Monticelli (1899). It will be noted that the present records of the parasite are from its usual host T. gurnardus and from a new host T. cuculus.

In a paper at present in the Press, we have endeavoured to show that where moderate or high infestations of men with Pediculus humanus corporis are present, the maintenance of these, and the level at which they tend to remain, are not dependent on the environment of the infested subject. The degree of infestation is a reflexion of the subject's recent standards of personal hygiene, and his habits at a given moment mould the structure of his infestation in the future.

1. The geographical distribution of cattle lice in Britain is recorded in detail. Bovicola bovis is the commonest and most widely distributed species in Britain.

2. The incubation period for the eggs was found to be: Haematopinus eurysternus, 9–19 days (av. 12); Bovicola bovis, 7–10 days (av. 8); Linognathus vitula, 10–13 days; Solenopotes capillatus, 10–13 days. With eggs of H. eurysternus it was found that the higher the minimum air temperature the shorter was the incubation period.

3. In H. eurysternus the average length of the instars was: 1st, 4 days; 2nd, 4 days; 3rd, 4 days; pre-oviposition period, 3–4 days. The average time for the complete life cycle, egg to egg, was 28 days.

4. The maximum longevity of H. eurysternus on the host was: males, 10 days; females, 16 days. No males or females of H. eurysternus survived a starvation period of 72 hr. at 20° C. and R.H. 70 or 0–10° C. and R.H. 70–85; but some nymphs survived this period at 20° C. and R.H. 70, but none survived 96 hr. starvation.

5. The maximum number of eggs recorded for one female was 24; and eggs were laid at the rate of 1–4 a day.

6. The threshold of development of the eggs of H. eurysternus appears to be about 27·5° C.

Over 3000 samples of hair from the scalp have been examined from four places in Africa and three in Asia. In every sample (except one small one) infestations of crab-lice (Phthirus pubis) were found; in each place they were found in less than 1% of heads.

The view is emphasized that the crab-louse has several ways of spreading through the human community.

The following is an account of the anatomy of the scolex of Aporhynchus norvegicus (Olss.) involving details of the musculature and nervous and excretory systems. The anatomy of the strobila has been described by Nybelin (1918). The specimens, mostly young complete strobilae, were obtained from the intestine of Spinax spinax caught in the deep-sea fishing grounds to the west of Ireland. Until recently the species had only been recorded from the coast of Norway, but in 1936 Joyeux & Baer found it in French waters. It was first described as Tetrarhynchus norvegicus by Olsson (1867), the genus Aporhynchus being created by Nybelin (1918) for the single species.

Elsewhere (paper in the Press) the author has shown that the majority of species originally described under Goniodes, although somewhat diverse in form, are fundamentally similar and cannot be separated generically. However, there are certain species originally placed in Goniodes which are generically distinct and should be separated. Among these is a group of species, forming the new genus described below, which is distinguished in both sexes by the small size of the first segment and the characters of the terminal segments of the abdomen and in the male by the form of the clavi.

1. The osmotic behaviour of three parasites in normal and experimental media has been studied with a view to understanding the relationship with their hosts.

2. Angusticaecum sp., a nematode frpm the intestine of the tortoise, is hypertonic in media of very low concentrations (1·1–1·3 % NaCl in tap water), but becomes isotonic in sea water and slightly hypertonic in 50 % sea water. Ligaturing experiments show that its cuticle is permeable to water and probably to salts.

3. Lernaeocera branchialis, a blood-feeding copepod from Gadus spp., is hypotonic to the surrounding sea water so long as it remains attached to its host, its blood showing an osmotic pressure equivalent to 2·O–2·8 % NaCl. Isotonicity with the medium is established when the parasite is excised and kept alive. Hypotonicity of Lernaeocera is probably caused by the low osmotic pressure of the blood of its host (1·443 % NaCl in Gadus pollachius), to which it is permanently attached.

4. Bopyrus squillarum, a blood-sucking isopod from Leander serratus, is isotonic or slightly hypotonic to sea water, the tendency towards hypotonicity being probably the result of the hypotonic nature of the blood of the host.

5. The osmotic properties of Lerpaeocera and Bopyrus would suggest their ability to survive in dilute sea water, a fact which is supported by their occurrence on hosts living in inshore or estuarine habitats.

1. The seasonal variations and regional distribution of the cattle lice have been studied by monthly examinations of cattle at the Cooper Field Research Station.

2. Additional evidence has been obtained by the distribution of a questionnaire to farmers, the general results of which are included in this paper.

3. The seasonal variations of the populations of the four species of cattle lice in Great Britain are similar. The maximum population density is reached in February and March. In April and May there is a rapid decline until the populations reach their lowest level in June, July and August. In September, the lice start increasing in numbers till they reach their maximum density in February and March.

4. The regional distribution of the population varies in accordance with the seasonal variations of the whole population.

5. The various climatic factors that may affect the lice populations are discussed. It is considered that the light intensity is a factor of major importance in this country.

6. The various factors inherent in the host animal are discussed, and it is suggested that the seasonal fluctuations of the density of the animal's coat are important.

7. The finding of a previous paper (Craufurd-Benson, 1941) that the microclimatic temperature is important as affecting the hatching of eggs is discussed in relation to the variations of lice populations as a whole.

In 1934 an intensive but unsuccessful search was made for the metacercariae of the Rhodometopa group of cercariae parasitizing Turritella communis Lamarck. Attention was concentrated on the vertebrate and invertebrate fauna of the Rame Mud, as Turritella has a patchy and circumscribed distribution in the Plymouth neighbourhood and is virtually restricted to a few small areas of ground in this region. The high rate of infection suggested that the metacercariae must occur commonly in some species found there, and the behaviour of the cercariae indicated that a fish served as second intermediate host (Rothschild, 1935, p. 169). This has now been proved.

1. In three previous papers (1936, 1938b, 1940a) the author has discussed the distribution of head-lice among their human hosts, his material being nearly 3000 complete crops of hair. The present paper deals with the strictly entomological side of the inquiry, that is to say, with the study of the populations of head-lice themselves. The total amount of material is the lice from 858 infestations from six places; from each of four places there were less than 100 infestations.

2. In about two-thirds of the infestations there were ten lice or less, the proportion of low infestations varying considerably from place to place (Table 1). Infestations over 100 never formed more than 10% of all the infestations in a place.

3. In a single head the proportion of the sexes is often far from equal; indeed, in light infestations it is common to find that all the adults are of one sex. Taking all the heads from one place, the total number of males and females differs significantly from equality, an excess of males occurring in one place, of females in another (Table 2). In all heads from one place the coefficient of correlation between the number of males and females is high, about 0·8–0·9. As the density of the louse population, does not generally affect the sex ratio, the correlation is approximately linear. But when the density is unusually high, as it is in some heads from Colombo, the proportion of males rises progressively. This is the only case known, in spite of much searching, in which sex ratio of the louse is affected by an environmental factor.

4. In the matter of the number of larvae per female, there are great individual differences between heads, though the coefficient of correlation, worked on all the heads from one place is as high as 0·7 or 0·9. Taking all the heads from one place, the mean number of larvae per female ranges between 5·4 and 10·9; many of the differences between places are significant. I have failed to find any explanation of these differences, and they do not seem to be affected by any environmental factor. The fact that the larvae are always more numerous than the females, indicates that there is a high mortality during the course of larval life; the author has failed to make a more precise estimate of the proportion which die.

5. A small part of the material was specially examined, and every larva referred to its instar. In this sample of 502 larvae it was found that the death-rate was higher in the third instar than in the other two, a state of affairs the reverse of what occurs in body-lice reared in boxes.

The metacercaria shown in Fig. 1 was obtained in the laboratory from Gobies (Gobius ruthensparri Euphras.) experimentally infected with a Pleurolophocerca cercaria from Peringia ulvae. This cercaria is regarded as the most interesting of all the Heterophyid larvae infecting this snail. It has been referred to briefly in a previous publication (Rothschild, 1938). It differs from typical Opisthorchid cercariae in the following characteristics:

(1) The lateral fin-folds are continuous and extend the whole length of the tail. The dorso-ventral fin-fold is reduced.

(2) The oesophagus and intestinal caeca (in addition to the pharynx) can be clearly made out.

(3) The cuticle is more heavily spined.

(4) The ventral sucker is better developed.

(5) The penetration gland ducts (fourteen in number) are not arranged in such definite bundles.

(6) Three acicular boring spines are present in the oral sucker.

In other respects the cercaria possesses the usual characters of the group.

Numerous specimens of a trematode which has proved to be a new species were collected from the kidneys of 'Ular sawa’ (Python reticulatus) at Alor Star and at Kedah, Malaya, by Mr G. B. Purvis, F.R.C.V.S. One batch comprises about 350 specimens, another one more than 150, and the entire collection of five batches exceeds 600 specimens. For this new species the name Styphlodora elegans is proposed. Mr Purvis also collected a single specimen of what seems to be a second new species from the stomach of the python at Alor Star, and for this the name Styphlodora compactum is proposed. Type specimens of the two new species are lodged in the British Museum (Natural History), London.

The hatching of the eggs of Pediculus humanus corporis De Geer is influenced by temperature.

High temperatures accelerate and low temperatures delay development.

The lowest constant temperature at which eggs will hatch is 24° and the highest 37°.

At 24° eggs begin to hatch on the seventeenth day and continue hatching until the twenty-first. At 37° eggs hatch on the sixth and seventh days. The temperature at which eggs hatch in the shortest time is 35° and the time 5 days. At these extremes many eggs are killed so that the percentages of successful hatches are very low. Eggs are killed by 2 days' exposure to 39°.

Temperatures at which the maximum number of eggs hatch he between 29 and 32°. In this range of “favourable” temperatures, up to 97% of successful hatches may be recorded. The incubation period is from 7 to 11 days. This is a convenient range of temperatures for laboratory purposes and gives largest numbers in a reasonably short time.

Newly deposited eggs will not hatch if kept for 14 days at 23° or for shorter periods at lower temperatures, until at 8° exposure for 7 days is sufficient to ensure that all eggs are dead.

If partially developed eggs are exposed to temperatures of 15° or lower, development ceases. If they are restored to a favourable temperature within 7 days, development is resumed and some of the eggs will hatch.

Older eggs which have almost reached hatching point at a “favourable” temperature hatch if transferred to temperatures as low as 18°. They do not hatch at 15° or lower if kept at such temperatures for at least 9 days.