The immature stages of Caraphractus cinctus Walker are described.

Four larval stages have been observed which may correspond to three or four instars. In no stage have mandibles been observed.

The first-instar larva is elongated and active. In the second-instar oral lobes are present. In the next stage the larva becomes shapeless and rather transparent. In the last stage the wall of the mid-gut shows conspicuous opaque spots which consist of single cells containing spherical concretions, probably the products of excretion.

These concretions later become free in the gut of the pupa and are discharged in the meconium when the imago emerges from the host egg.

The effects of parasitism on the host eggs of different ages is discussed. In newly laid host eggs all the contents are consumed by the parasitic larvae. In advanced eggs of Agabus the egg of Caraphractus is laid in the mid-gut of the host embryo where the parasitic larva develops, the hard parts of the host larva remaining intact. Parasitism in advanced eggs of Dytiscus is rarely successful.

The larvae of other Mymaridae are discussed and their main features compared. The first-instar larva of Caraphractus does not correspond to any of the previously described types of mymarid larvae.

The seasonal history is described, with the sequence of hosts parasitized throughout the year. From four to six generations of Caraphractus have been bred indoors during the year. The winter is passed as a diapausing prepupa. In some cases diapause may be prolonged. Fertility is high: 121 imagines have been bred from one female of Caraphractus.

I have much pleasure in acknowledging my gratitude to the late Dr W. D. Hincks for his kindness in reading the typescript of this paper: the comments by such a well-known authority on Mymaridae have been most valuable. I am very grateful to Mr O. Bakkendorf for allowing me to reproduce several of his figures of Mymarid larvae from the valuable work he devoted to the biology of Danish hymenopterous egg-parasites. I am also grateful to Miss B. A. Trott of the Commonwealth Institute of Entomology for the help she has so kindly given me with references.

Outdoor observations were made on the rate of development of the free-living stages of O. ostertagi at different times of the year, and on the migratory activities and longevity of the larvae in faeces, on herbage and in soil.

The effect of temperature on the rate of development of eggs and larvae in faeces, and the effect of temperature and humidity on the longevity of eggs and larvae when separated from faeces, were studied in the laboratory.

The results of these observations are discussed in relation to translation (that is, the process whereby eggs in faeces become infective larvae on herbage available to the grazing animal) and to the transmission of infection in the field.

I wish to thank Mr J. F. Michel for providing the infected faeces, and Mr D. A. Griffiths for technical assistance.

1. A qualitative and semi-quantitative analysis of the free amino acids in the haemolymph of Rhodnius prolixus has been made by paper chromatography.

2. Twenty-one amino acids or related compounds were detected of which histidine appears at the highest concentration.

3. The α-amino-N concentration of haemolymph is among the lowest values recorded for insect haemolymphs.

4. A substance corresponding in position to thyroxine has been detected in haemolymph of a few immature insects, and is formed if iodate is added to freshly withdrawn haemolymph.

I wish to record my great appreciation to the late Professor P. A. Buxton, C.M.G., F.R.S., for his valuable assistance and criticism during this study and to members of the staff for helpful discussions. The study forms part of a Thesis for the degree of Ph.D. approved by the University of London, and was financed by the South African Council for Scientific and Industrial Research whose generous support I acknowledge with pleasure.

1. A qualitative paper chromatographic analysis of the free amino acids in Rhodnius urine and excreta was made: eleven amino acids or related compounds were detected, cystine and cysteic acid in urine, and histidine, histamine, leucine, taurine, glycine, valine, phenylalanine and alanine in the excretory fractions.

2. In addition to these, three yellow pigment spots were separated from the excreta; one of these is of unknown composition and two are peptides.

3. A possible relationship between certain of the excretory amino acids and haemolymph ones is discussed.

I am greatly indebted to the late Professor P. A. Buxton, C.M.G., F.R.S., for his stimulating criticism during this study, and to the members of the School for very useful discussion, and to Mr Paul Baily for performing the column chromatographic analyses on my behalf. The study forms part of a Thesis for the degree of Ph.D. approved by the University of London, and was financed by the South African Council for Scientific and Industrial Research. I wish to acknowledge their generous financial support.

Third and artificially hatched second-stage larvae of A. suum were exposed to the action of saline and normal and homologous immune pig serum. Precipitates developed at the mouth, excretory pore, anus and around the cuticle of third-stage larvae when they were placed in immune pig serum, but not in saline or normal serum. Precipitate was most evident at the excretory pore and was often the first precipitate to form. It is suggested that the excretory products may play an important role in stimulating the production of antibody in the host. A relationship was noted between the antibody titre of the serum and the amount of precipitate, the life span of the larvae, their activity, and the rate at which precipitates formed. It is concluded that the titre of the serum was in some degree a measure of the ability of the host to resist reinfection.

Circumlarval precipitates did not form when second-stage larvae were placed in samples of the same immune serum. It is pointed out that this may be due to the lack of sufficient antigenic material available to react with antibody in the antisera. It is also suggested that an absence of sufficient larval antigen may also partly account for the small degree of resistance exhibited by the resistant host within the first 2 or 3 days of reinfection.

The work, which is abstracted from a Ph.D. thesis, was carried out in 1957 under the tenure of an Animal Health Trust Wellcome Fellowship. I am grateful to Dr Soulsby, under whose guidance this work was carried out.

1. Studies have been made of carbohydrate metabolism in Fasciola gigantica during starvation and these are compared with data available about carbohydrate metabolism in F. hepatica.

2. In F. gigantica the glycogen content before starvation was 5·4% of f.w. or 25·35% of D.W. of tissue, and the glycogen content after starvation was 3·5% of F.W. or 16·29% of D.W. of tissue.

3. The medium in which F. gigantica was incubated was analysed for lactic acid as one of the end products of glycogen consumption. The lactic acid given out in a period of 2 hr. was 0·46% of F.W. or 2·18% of D.W. of tissue.

I wish to thank Professor K. Sahai for his generous help in the preparation of this manuscript.

An in vivo test is described for the screening of compounds for anthelmintic activity using Hymenolepsis nana var fraterna in mice. Results obtained with known taenicides and taenifuges are tabled, analysed and compared with their action against the tapeworms of larger animals including man.

My thanks are due to Messrs Boots Pure Drug Co. for permission to publish, Mr J. W. G. Leiper, F.R.C.V.S. for his help and advice, and Miss J. Smith for her able technical assistance.

The LD50 of Nippostrongylus muris for outbred hooded rats has been estimated. It was higher for males than for females and this does not appear to be due to weight differences. The distribution of times of death was bimodal; the peaks corresponding to different stages in the life cycle of the worm.

We wish to thank Mrs M. Whitehead for technical assistance and Mr I. McDonald for statistical analysis.

Rats were given immunizing doses of N. muris larvae by three different routes: orally and intraperitoneally and through the skin. The immunized rats survived a test infection which was lethal for non-immune rats. Only the rats immunized by the skin route showed skin sensitivity.

Two attempts to transfer immunity against N. muris to rats using the lymph node and spleen cells from actively immunized donors were unsuccessful. Experiments showed that the rats were sufficiently inbred, that the transfer technique was satisfactory, and that the donors were adequately immunized. The rats' competence as donors for adoptive transfer was demonstrated with sheep red cells as antigen. The adoptive transfer of immunity against sheep red cells was successful in recipients whose donors had sheep red cells only and no N. muris. There was no detectable transfer of immunity against N. muris or sheep red cells to recipients whose donors had received both.

We are very grateful to Miss Kathleen O'Brien for technical assistance, to Professor P. B. Medawar, F.R.S., for his help and advice and to Dr E. J. Delorme for showing us Professor M. F. A. Woodruff's skin-grafting technique.

In 1951 the laboratory examination of birds at Fair Isle Bird Observatory was extended to include the collection of ectoparasites. The fleas collected during the years 1951–55 have been recorded by Rothschild (1958).

1. The means of attachment of the mite Myocoptes musculinus to the hair of the host, the mouse, and the sites where it is located are given.

2. Normal and skin infected with M. musculinus of young (6–8 weeks) and adult (6 months) mice is treated with colchicine and examined histologically.

3. Infected skin shows a mitotic count of approximately four times that of normal skin in the adult; there is no appreciable difference in the young.

4. Acaricides used to control the mite were benzene hexachloride (0·015%), dieldrin (0·015%), arsenic and sulphur mixture (0·018% arsenic), piperonyl butoxide (5%) and dimethylphthalate (100%); the latter being the most efficacious.

5. It is established that the drugs had no effect on the rate of division of the cells of the malpighian layer of the skin.

6. The number of Myobia present increases as the Myocoptes are killed unless dimethylphthalate, an oily liquid, is used at intervals.

7. Diet in conjunction with signs of mange is discussed.

8. Carriers of M. musculinus are given.

I wish to thank Cooper McDougall for supplying the materials used in dipping and swabbing, and the Infestation Control Laboratory of the Ministry of Agriculture for supplying me with a number of specimens of wild mice from different parts of the country. I am also grateful to the Council of the Royal Free Hospital School of Medicine for facilities for carrying out the work; and to Dr A. M. Hughes for her helpful guidance at all stages of the work and especially for reading the paper.

1. The eggs of Thelastoma bulhõesi are shown to have a sticky outer coat of acid mucopolysaccharide.

2. The acid mucopolysaccharide is secreted by the lower uterus wall and by the vagina uterina.

3. A protein substance of unknown function has been observed in invaginations in the ovijector of T. bulhõesi.

4. This protein substance appears to be secreted by the lower part of the vagina uterina and passed along into the ovijector.

5. Possible functions of the mucopolysaccharide coat on the eggs, and of the protein substance in the ovijector, are discussed.

I wish to express my thanks to Dr P. Tate for many invaluable suggestions and for his constant encouragement during this investigation.

1. A description is given of the egg of Gasterophilus intestinalis.

2. The chorion has been shown to consist of a number of tanned protein and lipoprotein layers.

3. The waterproofing of the egg is shown to be dependent on a primary wax layer on the inner membrane of the endochorion and a secondary layer on the vitelline membrane.

4. The respiratory requirements of the egg are supplied from a free-air space between the inner membrane and the tanned protein layer of the endochorion which communicates with the atmosphere by specialized pore canals opening into the follicular grooves.

Thanks are due to Dr P. Tate for suggesting the subject of this work and for his advice and encouragement during its progress.

Definition. Oxyurinae—mouth with three small lips; cuticle with or without lateral flanges; vestibule absent; oesophagus with a posterior globular bulb containing a valvular apparatus and separated from the rest of the oesophagus by a slight constriction; excretory pore behind the oesophageal bulb; posterior extremity of the body in both sexes obliquely truncate ventrally at the level of the anus, rounded and prolonged as a long subulate tail which is provided with spines or smooth.

When specimens of the turtle, Trionyx gangeticus, and of the fish, Wallago attu, were purchased in a local market and examined, nematodes were found in the intestines of both these hosts. Two males were found in the intestine of the turtle, and a male and three females in the intestine of the fish. Examination of these nematodes showed that they all belonged to the genus Dichelyne Jägerskiöld, 1902, but that none of them belonged to any known species of this genus. The genus Dichelyne was regarded by Yorke & Maplestone (1926) as being synonymous with the genus Cucullanus, O. F. Mueller, 1777, but was later re-instated as a distinct genus by J. F. Mueller (1934), who reduced the genus Dacnitoides Ward & Magath, 1916, to synonymy with Dichelyne. In the light of these emendations the genus Dichelyne now includes the following species: D. fossor Jägerskiöld, 1902, 1909; D. cotylophora (Ward & Magath, 1916), J. F. Mueller, 1934; D. robusta Van Cleave & Mueller, 1932; D. fastigatus Chandler, 1937; and D. diplocaecum Chandler, 1937.

1. Echinobothrium acanthinophyllum sp.nov. occurs in the spiral valve of Raja montagui Fowler. E. affine Diesing was also present.

2. E. acanthinophyllum possesses 23 large hooks in each apical group flanked by 4 small hooks on either side. There are 13 spines in each of the 8 longitudinal rows on the cephalic peduncle and 13 testes in each proglottid. The ripe eggs aggregate into clusters of 8–10, which fill the gravid uterus.

3. Euzet's key is revised to include the 9 species of the genus.

Records of non-sporozoan Protozoa occurring in the hind-gut of cockroaches are summarized.

The Protozoa studied were the three flagellates Lophomonas striata, L. blattarum, Monocercomonoides orthopterorum; the rhizopod Endamoeba blattae, and the ciliate Nyctotherus ovalis, in the cockroaches Periplaneta americana, P. australasiae, Blatta orientalis, Blattella germanica and Blaberus giganteus.

Specimens of Blatta and Periplaneta americana were maintained at 37° and 25°C. under extreme conditions of humidity. Maximum humidity enabled the host, and the Nyctotherus which it harboured to survive for a longer time. The results of the experiments indicated that the well-being of the protozoan parasites is closely linked to that of the host.

Periplaneta americana, Blatta, Blatella and Blaberus were subjected to pure oxygen at 3½ atmospheres pressure and the effect on the Protozoa observed. The flagellates were killed first, then Endamoeba and lastly Nyctotherus. They survived in Blatta for a longer time than in Periplaneta; and Nyctotherus in Blaberus and Blattella sometimes survived the hosts. The hosts appeared to act as a barrier against poisoning by oxygen, and the strength of the barrier varied in the different species of cockroaches.

Nymphal Periplaneta or Blatta which were about to moult underwent a period of self-starvation which lasted for up to 10 days. The period was terminated by the moult: at this time, the little food that was in the gut was very dry. All species of Protozoa could survive these conditions, but Nyctotherus seemed to be the most hardy. The main mass of ciliates seemed to be nearer to the anus than in the non-moulting cockroach. Many of the ciliates were often clumped together into a ‘raspberry’. The bodies of the individual ciliates were more spherical than usual, but those in the ‘raspberry’ were moulded into polygonal shapes. The macronucleus underwent a change in form which revealed that its basic structure is that of a folded sheet.

The changes were reversed within 24 hr. They could not be induced by experimentally imposed conditions of starvation or dehydration of the hind-gut. The changes in Nyctotherus ovalis are contrasted with the sexual stages occurring in N. cordiformis and in the Protozoa of Cryptocercus.

This work was done during the tenure of a Research Studentship awarded by the Agricultural Research Council. I am deeply indebted to Dr P. Tate for his encouragement and counsel at all stages of the work. I wish to thank Drs J. Barker and E. R. Turner, of the Cambridge University Botany School, for the loan of the apparatus used in subjecting cockroaches to oxygen under pressure, and Mr A. C. Bloy, of the Zoology Department, for gifts of cockroaches. I am most grateful to Mrs E. F. M. Hawkins and Mr B. H. Baker for technical assistance.

The size and shape of the trophozoite of Nyctotherus ovalis in different species of cockroaches was found to vary considerably, and this was attributed chiefly to the presence or absence of large paraglycogen granules within the ciliate.

The size and shape of the cysts of N. ovalis which were passed in the faeces of the host on successive days were found to fluctuate around means which were more or less constant over a long period. The constants varied according to the species of the host: the largest and fattest cysts were found in the faeces from Blatta, the smallest and most slender from Blattella. Those from Blaberus were of the Blattella-type, but Periplaneta harboured populations which gave rise either to the Blatta-type of cysts or to the Blattella-type.

The constant size and shape of the cysts was not altered when the host moulted, but there was always a decrease in size and sometimes a change of shape when an infection was established in a new host. The cause of these changes is unknown. An increase in size was induced by an increase in environmental temperature, but the size declined during a subsequent period at lower temperatures. The work of other authors on changes in the sizes of protozoan cysts is discussed.

The cyst wall of N. ovalis consists of four separate layers plus an outer membrane. They all seemed to be proteinaceous in nature. Treatment with various inorganic reagents and proteolytic enzymes revealed that the knob is the most easily destroyed part of the wall. A histochemical test for keratin showed that this is the chief constituent of the wall. The keratin appeared to be least organized in the knob, and hence the knob is the least impermeable part of the wall.

This work was done during the tenure of a Research Studentship awarded by the Agricultural Research Council. I am deeply indebted to Dr P. Tate for his encouragement and counsel at all stages of the work.

The only mode of transmission of Nyctotherus ovalis from one cockroach to another was shown experimentally to be by way of ingestion of the encysted stage of the ciliate. The cysts were remarkably resistant, being able to remain viable for 21 weeks at −18°C. if kept in dry faeces, or for 20 weeks in wet faeces at 4°–25°C. Their life was much shorter if kept at 37°, 25°, or 4°C. under dry conditions, or at −18°C. under wet. The cysts could withstand freeze-drying, or storage in pure oxygen, carbon dioxide or nitrogen, at least for short periods.

Nyctotherus ovalis could excyst in any of the four species of cockroach which were tested (Periplaneta americana, Blatta orientalis, Blattella germanica, Blaberus giganteus), irrespective of the species of origin. The ciliate could establish an infection in a very young host; in a host which had ingested infected faeces once only; in hosts which were in a very dry or a very humid environment; in a host maintained at a temperature far below that required for in vitro excystation, subject only to the temperature being high enough for it to be possible for the cockroach to digest its meal; but Nyctotherus could not establish an infection in cockroaches which were about to moult, because there was no movement nor digestion of food in the gut. There was no evidence of an instinctive drive on the part of the cockroach to eat infected faeces. There was some evidence that the Blatta and Blattella types of trophozoite and cyst were associated with the presence or absence respectively of a type of flora typically associated with the hind-gut of Blatta.

The process of excystation took as little as 3 hr. for completion in vivo, but this time was increased if faecal material was ingested along with cysts. The process was most rapid in the smallest cockroach (Blattella) and slowest in the largest (Blaberus). The process, once started, could be completed in vitro, but at a considerably slower pace. Digestion of the knob on the cyst by the cockroach's enzymes seemed to be necessary if the ciliate was to emerge.

A small proportion of cysts hatched after passage through the gut of a locust, but no means were found of increasing this proportion, and an infection was never established. Excystation did not occur in any other arthropod, nor in the frog, which were tested.

Cysts recovered from the mid-gut of a cockroach completed the process of excystation in vivo more rapidly if they were put in a buffer medium of pH approximating that of the mid-gut than if they were put in saline. Passage of the cysts through the foregut of the cockroach had no function in stimulating excystation: the agent seemed to be the trypsin secreted by the mid-gut caeca, or the products of its activity. The many failures in the series of experiments which are reported here can probably be attributed to contaminating bacteria.

The complete process of excystation could occur in vitro if the cysts were incubated with faecal matter from the cockroach. The optimum temperature was 32°C., and 2 days were needed for a significant number to hatch. No means were found of shortening this time, nor any agents which could be substituted for the faecal matter. The stimulus seemed to be provided by particular anaerobic bacteria of the faeces which were present in some cockroaches, but absent in others.

Work by other authors on excystation in other Protozoa is reviewed. It was concluded that in vivo excystation of Nyctotherus ovalis occurs as a result of stimulation of the cyst by the digestive trypsin of the cockroach, and not by the products of the unidentified bacterium which is active in vitro. Cysts originating from Blaberus seemed to be less sensitive to this bacterial factor than some of those from Periplaneta or Blatta.

This work was done during the tenure of a Research Studentship awarded by by the Agricultural Research Council. I am deeply indebted to Dr P. Tate for his encouragement and counsel at all stages of the work.