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Ratios of D-alloisoleucine to L-isoleucine have been determined on freshwater molluscs from 13 interglacial sites in South East England and on marine molluscs and foraminifera from 10 Pleistocene and Upper Pliocene Crag sites in East Anglia. We can distinguish the Ipswichian, then either one or two interglacials that may be younger than the classical Hoxnian, then the Pleistocene Crags, then the Pliocene Coralline Crag.

A complex of several genetic factors determines the susceptibility of juvenile Biomphalaria glabratus to infection by Schistosoma mansoni. A simple dominant factor can cause juvenile susceptible snails to become refractory to the parasite at maturity. Stocks of such adults may prove to be of use in genetic control of S. mansoni in endemic areas.

The expression of similar antigenic determinants by trematode parasites and their intermediate (invertebrate) or definitive (vertebrate) hosts has been previously reported. Studies of experimental and human infection by the parasite Schistosoma mansoni have revealed the strong immunogenicity of a surface antigen with a relative molecular mass (Mr) 38,000 (38K). Here we provide evidence that the important protective epitope of the 38K molecule is expressed by the uninfected intermediate host of S. mansoni, Biomphalaria glabrata and is synthesized both by the mollusc and by the parasite throughout its life cycle, thus confirming our original hypothesis. Deglycosylation experiments indicate that the protective epitope is an oligosaccharide and in B. glabrata, is associated with a 90K component. Analysis of soluble extracts from different freshwater mollusc species shows that the same protective epitope is found in schistosome as well as in non-schistosome hosts. Moreover, it was also found on the haemocyanin of the keyhole limpet (Megathura crenulata), a carrier protein widely used in immunological studies.

I HAVE recently demonstrated1 that penetration of Fasciola hepatica into Limnaea truncatula is a brief but elaborate process which involves the successful attachment of the miracidium to the snail, seemingly by suctorial adhesion, and the production of a secretion which cytolyses the integument of the snail in a circumscribed area underlying the anterior non-ciliated pit of the larva. Not until the snail's epithelium has been perforated by cytolytic action does the larval trematode thrust itself into the snail's body. By the time these preparations for entry have been completed, the miracidium has cast off its ciliated epithelium, so that although it is the miracidium which attacks the snail, it is the young sporocyst which enters the snail's body.

IT has recently been shown that antagonistic interaction, takes place when schistosome, strigeid or plagiorchiid sporocysts occur together with certain echinostome rediae in the same snail1. This interaction results in the total elimination of the first three groups of parasites. This communication discusses the antagonistic interaction between sporocysts of Schistosoma mansoni Sambon and rediae of an unidentified Echinostoma species in the snail Australorbis glabratus (Say).

Children in Siavonga, a tourist centre on the Zambian side of Lake Kariba, have been found to be infected with both urinary and intestinal schistosomiasis, indicating that there is active transmission of the diseases in the area. The snails involved seem to be Bulinus africanus and Biomphalaria pfeifferi, and it is suggested that mats of the water weed Salvinia auriculata could provide microhabitats for colonies of the snail and thereby provide foci for the transmission of the diseases.

THOUSANDS of snails infected with trematodes have been surveyed in the Kuala Lumpur area1–5. Lymnaea rubiginosa (Michelin), the commonest and most carefully studied snail, is infected with at least thirteen species of trematode larvae: four echinostomes, three plagiorchids, two strigeids, one Spirorchis, one Trichobilharzia, one Fasciola and one psilostome. Multiple infections were, however, very rare and certain trematode combinations were not found7 and none of the few double infections found involved species with redial development2. The only double infections found were those in which both parasites underwent sporocyst development (producing strigeid and schistosome furcocercous or plagiorchid xiphidiocercous cercariae, personal communication from K. J. Lie).

MEASURES to control schistosomiasis (bilharziasis) aimed at either the molluscan vector or the trematode's larval stages might be enhanced by a better understanding of the intricacies of how miracidia and cercariae find and penetrate hosts. Previous work from our laboratory identified chemicals from mammalian skin that initiated penetration responses by Schistosoma mansoni cercariae1. Other earlier studies implicated amino acids and additional compounds as attractants of S. mansoni miracidia to the molluscan host, but did not show that these substances were derived from the snail2. Subsequently, based on Neuhaus'3 and C. A. Wright's4 indications that snails release substances into water that stimulate miracidia, several investigators5–8 have confirmed that snails ‘condition’ water making it stimulatory or attractive to miracidia. Wright and Ronald9 recently demonstrated that water conditioned by the snail Lymnaea palustris attracted miracidia of the rodent blood fluke, Schistosomatium douthitti, and that this snail-conditioned water (SCW) contained amino acids. Here we show that Biomphalaria glabrata, the molluscan vector of S. mansoni, the important parasite of humans, contributes amino acids to the aqueous environment, and that these, and possibly other substances elicit chemotactic and chemokinetic responses by miracidia of this parasite.

PREVIOUS work on a naturally occurring substance which inhibits growth in Biomphalaria sudanica1 indicated that its toxicity was partly due to its surface activity. It was therefore decided to test various commercially produced surface-active agents, at various concentrations, on the survival of this species of snail.

IT has been known for more than a century that a snail may be infected with more than one species of larval trematode. The elaborate field investigations of Cort et al.1 showed that certain combinations of trematode species were compatible with each other, while other combinations occurred rarely or never. Ewers's2 work suggested that infection with a certain trematode might predispose the snails to infection with another species.

IT is well known that the larval trematode “Diplostomum volvens Nordmann, 1832” may cause impaired vision, and even blindness, in certain fishes. Rushton1 and Baylis2 have reported the presence of this diplostomulum in the eyes of rainbow trout in Britain. The presence of 20–40 parasites in the lens of each eye may favour completion of the life-cycle, because the fish then falls an easier prey to water birds. The definitive hosts of this trematode, Diplostomum spathaceum (Rudolphi, 1819), are various species of gulls, and the usual location is the intestines3.

Active Transport of Alkaline Earth Ions as Physiological Base of the Accumulation of Some Radionuclides in Freshwater Molluscs

IN a recent communication, McCullough1 stated that although the snail Bulinus (Pyrgophysa) forskalii was known to be a vector of urinary bilharzia in the Gambia and in Mauritius, there was no direct evidence that it acted in a similar capacity in the Gold Coast; moreover, snails of that species collected in the Gold Coast were wholly resistant to experimental attempts to infect them with the miracidia of the causative organism, Schistosoma haematobium.

Schistosoma mansoni is a parasitic flatworm transmitted by snails which infects millions of people in tropical countries with poor sanitation, where new irrigation schemes, population growth and continued poverty have increased the prevalence of infection. Larval worms, emerging from freshwater snails, penetrate human skin and mature in intestinal veins where they lay eggs. Many eggs remain in and damage tissues while others pass out in excreta and hatch in water, releasing embryos called miracidia. These short lived, multicellular, ciliated, free-swimming miracidia must find, penetrate and reproduce within certain snails whence emerge the larvae infective for man. Snails emit substances (“miraxones”) which alter the swimming behaviour of miracidia and may help them to locate and attack the snails1–3. Miracidial behaviour is reportedly affected by snail-elaborated amino acids4,5 and by various other agents, including fatty acids6,7. We now report that magnesium appears in water in which uninfected Biomphalaria glabrata (a snail host of Schistosoma mansoni) is confined, and that magnesium ions alter miracidial swimming patterns.

Freshwater Fishes of the U.S.S.R. and Adjacent Countries Vol. 3. By L. S. Berg. Translated from the Russian. Fourth edition. Pp. 510. (Jerusalem: Israel Program for Scientific Translations; London: Oldbourne Press, 1965.) 108s.

WHILE engaged in researches on larval trematodes in The Netherlands, I collected specimens of the snail Paludina vivipara Lm. from a dried-up waterway in the vicinity of Houten (Province of Utrecht). In the course of routine examination, no cercariae having been given off by the snails under laboratory conditions, they were dissected and large numbers of rediae found which proved, by their structure and measurements, to be the larval stage of an amphistome. This is in itself unusual as P. vivipara is not recorded as acting as intermediate host for this group of trematodes.

THE genus Apatemon has been recorded frequently from members of the Anatidae in Europe and the United States1,2. In Britain only one published record of this genus seems to be available. Baylis3 recorded Apatemon gracilis (Rudolphi, 1819) from Anas penelope from Cheshire. Two unpublished records exist of the occurrence of this species in Wales. Davies4 described this species from a domestic duck, and Williams5 recovered 12 specimens of Apatemon gracilis (Rudolphi, 1819) from Anas crecca and 15 specimens from Anas penelope. The host–parasite lists of Nicoll6 are not considered valid in this context as they do not differentiate between European and British records.

Lymnaea (Pseudosuccinea) columella Say 1817, described from specimens probably obtained in the vicinity of Philadelphia1, is widely distributed in still and slow-flowing waters in the eastern United States of America, Mexico, Central America, Cuba and the northern and central regions of South America1,2. Fossil specimens are known from the Pleistocene of North America, and another species of the sub-genus has been described from the Pliocene of the same region3. L. columella is believed to have been introduced by human agency, probably with aquatic plants, into Puerto Rico, Tenerife, South Africa and many European countries4.

As a first step in providing a suitable medium for in vitro culture of snail-borne stages of trematode parasites, we have developed a suitable medium for in vitro culture of snail cells and tissues. The culture medium devised and tested in our laboratory is capable of sustaining cells and promoting growth for as long as 60 days. Presumably it will maintain snail cells and tissues for a much longer time, but lack of media has prevented us from running longer experiments.

DURING my journey up the Fitzroy River with the surveying party from King's Sound to the Leopold Ranges (between lat. 17° 4′ and 18° 20′ S.), I observed many specimens of sword- and saw-fish. They appeared at intervals the whole way up the river, but none observed were more than three feet or three feet six inches long. About 300 miles up on the Margaret River I procured the saw of a small one. It measures about nine inches long and two inches wide. A few days after this, a little higher up the river, some of our men found a shark five feet long, and recently killed, probably by natives. I could not visit the place, as we were then about to break up camp for our return, but the men showed us some of the teeth, which were unmistakably those of a shark. They were, besides, well acquainted with the appearance of that fish.

IN a recent paper Cridland1 has stated among his conclusions that there is no evidence for the occurrence of strains in human schistosomes and also that he had found that certain species of snail did not appear to act as carriers. For example, he states that Bulinus africanus ovoideus (Bgt.) will not act as a carrier of Schistosoma haematobium in Uganda, on the evidence that he had not been able to infect it in the laboratory. In the Kitui area of Kenya Bulinus (Physopsis) africanus ovoideus (Bgt.) and B. (P.) nasutus (von Marts.) both occur in ponds, dams and streams. The latter snail is common also in the coastal regions of north-east Tanganyika and is, in my opinion, quite different from the snail occurring in the Great Lakes which Mandahl–Barth2 recorded as nasutus. He agrees with me that different sub-species are involved.

THE possibility of British species of Lymnaea, other than L. truncatula, acting as vectors of Fasciola hepatica has remained a moot point since Thomas1, in 1883, observed the miracidia to penetrate young specimens of L. pereger. The observation of Noller and Sprehn2, in 1924, added to the uncertainty, when by dissection of a young specimen of L. stagnalis they actually secured cercarise that were sufficiently far developed to show the lateral glands. As a result of experiments recently carried out at Weybridge, it can now be stated with certainty that F. hepatica is capable of completing its development in L. stagnalis with the ultimate emergence of cercariae, which encyst and are capable of producing fluke infestation in mammals.

THE process of excystment of the metacercariae of digenetic trematodes has not been examined in great detail. Most experimental work so far has been concentrated on the effect of artificial gastric and intestinal juices.

IN recent years, detailed studies have been conducted on schistosomiasis and its snail vectors in the Gold Coast. The results of surveys throughout the territory show that although Schistosoma haematobium and S. mansoni are both endemic, the former infection, together with its snail hosts, Physopsis africana and Bulinus sp., sensu stricto, is considerably more widespread than the latter and its planorbid vector, Biomphalaria pfeifferi1.

INTESTINAL bilharzia (caused by the trematode Schistosoma mansoni) is transmitted by snails of the genus Biomphalaria. A survey has recently been conducted to determine the distribution of these snails in the Khartoum and Blue Nile provinces of Sudan.

Key to Parasites of Freshwater Fish of the U.S.S.R. Compiled by I. E. Bykhovskaya-Pavlovskaya et al. Translated from the Russian. Pp. viii + 919. (Jerusalem : Israel Program for Scientific Translations; London: Oldbourne Press, 1964.) 180s.

SNAILS of the sub-genus Bulinus (Physopsis) are known to be the principal intermediate hosts of Schistosoma haematobium in East Africa. There are several species present, and of these B.(P.) africanus is represented by B.(P.) africanus ovoideus (Bourguignat) which is widely distributed throughout the area. Mandahl-Barth1 suspected that B.(P.) africanus africanus (Krauss), the subspecies found in southern Africa, also occurred in southern Tanganyika. He considered that the description of ‘Physopsis rekawaensis’, from Lake Rukwa in south-west Tanganyika, did not differessentially from the typical B. (P.) africanus africanus. This communication records the finding of B.(P.) africanus africanus along the Little Ruaha River valley near Iringa (altitude 5,500 ft. above sea-level) in the southern highlands of Tanganyika. Dr. Mandahl-Barth kindly identified these snails.

THE amphibious snail Lymnaea truncatula, which serves as an intermediate host of the liver fluke, Fasciola hepatica, has been found in the past to be somewhat difficult to maintain in laboratory culture. In connexion with current work on the epidemiology of the severe disease of grazing animals which is caused by this parasite, one of our first problems was to establish satisfactory means of culturing the snail. Our attempts have proved so far successful that we are able to grow the snails in unlimited numbers, at different seasons of the year and to a larger size than they usually attain in their natural habitat.

An Introduction to Molluscan Ecology Distribution and Population Studies of Fresh-water Molluscs. By Dr. Alan Mozley. Pp. + 72. (London: H. K. Lewis and Co., Ltd., 1954.) 9s. net.

3:5-Dihalogeno-4-Hydroxybenzonitriles as Herbicides: 3 : 5-Dihalogeno-4-Hydroxybenzonitriles : New Herbicides with Molluscicidal Activity

NOT since 1933 has the annual rainfall in Natal approached the low figure of the last two years except in 1941, and more than half the annual total for 1945, namely, 27.1 in. up to December 26 (when some rains started), fell in the months of February and March.

Limnaea stagnalis collected from three sources in the vicinity of Winches Farm Field Station of the London School of Hygiene and Tropical Medicine were found to be shedding furcocercous cereariae. On emergence from the snail, the cercariae swam freely for a short time with either the head- or tail-end forward and then attached themselves to the side of a beaker nearest the light. The cercariae were apharyngeal, possessed a pair of eyespots and had six pairs of flame cells in the body and one pair at the base of the tail. The posterior part of the body was taken up by five pairs of penetration glands, the two anterior pairs having coarsely granular and the three posterior pairs having finely granular contents. In its behaviour and morphological characters the cercaria is identical with that described as C. ocellata by Rees1 and Taylor and Bayliss2, who have given a detailed description of the cercaria which will not be repeated here. At one site (Verulamium Lake) a small percentage of Limnaea ovata were occasionally found to be shedding this cercaria. In both hosts the sporocysts were located in the digestive gland.

As a mere sciolist in geology it sometimes occurs to me to wonder whether enough attention has been given to the distribution of freshwater fauna, in estimating the origin of British land contours and the course of rivers. It is generally accepted that until the North Sea was formed by an extensive subsidence of land in an age not geologically remote, all eastward-flowing rivers south of and including the Yorkshire Ouse were tributaries of the Rhine. The natural result of this should be that the fishes of the Rhine should continue to inhabit its ancient tributaries, as in fact they do in all rivers between and including the Ouse of Norfolk, the Ouse of Yorkshire, and the Trent system. But there is a notable absence from the Thames and the Medway of two species common to the aforesaid rivers and the Rhine—namely, the burbot or eel-pout (Lota vulgaris) and the grayling (Thymallus vulgaris).

PREVIOUS workers1 have reported that only the male of Schistosoma spindale develops in the guinea pig. Fairley, Mackie and Jesudasan, who carried out a detailed investigation, suggested that “some peculiar host reaction to the less robust female schistosome probably underlies this phenomenon in the case of S. spindale”. A comprehensive study was undertaken of this apparent immunity to only one sex of a metazoan parasite, as a result of which it has been found that female S. spindale also develops in the guinea pig.