The distribution of the integumentary papillae of the cercaria of Himasthla secunda has been studied by a variety of techniques. Structures stained by silver nitrate and visible under the light microscope correspond in their spatial distribution with papillae observed under the scanning electron microscope. The tegumentary papillae described with the light and scanning electron microscope are correlated with the specialized nerve endings in the tegument as seen in transmission electron microscopy. The ultrastructure of these papillae is examined by conventional transmission electron microscopy and the probability that these structures are sensory is discussed.

Merocysts in P. inornatus are found in the liver, spleen and lungs, while in P. magnificus the liver is the only site. In the former the protoplasmic rim is narrow and the merozoites are sparsely distributed within it; in the latter the protoplasmic rim is irregular, quite thick and broken in places. In the former, the colloidal mass is scanty, and is in the form of tenuous matrix enclosing irregular interspaces; in the latter form, the colloidal mass is in the form of homogeneous substance with little vacuolation. In view of the wide differences in the structure and the site of occurrence, the merocysts found in the two different species of flying squirrels are considered to belong to two separate parasites. The parasite occurring in P. inornatus is identified as H. rayi rayi Tokura & Wu, sensu stricto, while the other parasite occurring in P. magnificus is designated H. rayi wui, a new subspecies, named in honour of Dr Wu Chen-Lan who worked on flying squirrel malaria in Formosa.

The changes in the percentage chemical composition of both complete strobilae, and of the immature, mature, and gravid regions of the strobila of Hymenolepis diminuta have been studied during development of the worms from 5 to 16 days postinfection. The chemical components that have been evaluated are non-protein nitrogen, protein nitrogen, ribonucleic acid, deoxyribonucleic acid, lyo-glycogen, desmo-glycogen and total lipid.

While the nitrogen, RNA and DNA fractions, expressed as μg/mg of worm dry weight, all decreased markedly with increasing worm age and size, the carbohydrate and lipid fractions increased over the same period of development.

In worms up to 7 days old there is a high non-protein nitrogen value, high RNA and DNA fractions, the lyo-glycogen component of the total carbohydrate is very large, but the amount of carbohydrate expressed as a percentage of dry weight is low. These values are associated with the very high rate of metabolism of the young worms. From 7 to 16 days postinfection the rate of growth slows considerably, which is reflected in the corresponding decreases in the non-protein nitrogen, RNA and DNA fractions, and the increase in the total carbohydrate percentage.

The changes in the chemical composition along a complete strobila complement the morphological evidence as the emphasis switches from segmentation to tissue differentiation and organ maturation.

The changes with age in the percentage composition of the same region of the strobila show that neither the complete worms nor the different regions of a strobila are static in terms of their chemical components, but are changing systems which may be correlated with the ontogenetic development and migrational behaviour of the worms.

The karyotypes of five species of Glossina are described.

Differences were found between karyotypes of different species, and also between different populations of the same species. These differences are discussed in relation to the phylogeny of the genus.

A new species of ascaridoid nematode, Baylisascaris tasmaniensis, is described from three marsupial carnivores of Tasmania, namely Sarcophilus harrisi, Dasyurus viverrinus, and Dasyurops maculatus. The new species is differentiated from other species in the genus Baylisascaris and the phylogenetic affinities within the genus are discussed in relation to the origin of the placental and marsupial carnivores.

Heavy infections of E. acervulina result in a depression in body weight of the host, but anorexia induced by the disease is not the only factor responsible for this, since normal birds starved to the same extent did not lose as much weight. It was shown that the absorption of l-histidine and glucose from the infected part of the small intestine was depressed and may be a contributory factor to this weight loss; restricted feed intake alone tended to increase, rather than decrease, absorption.

Changes in plasma glucose and lactate and glycogen stores of cardiac and voluntary muscle have been determined during the course of an infection by Eimeria tenella.

No hyperglycaemia resulted nor was there any significant change in the stores of hepatic glycogen during the period of observation.

There was a significant reduction in the plasma lactate concentration on the 1st and 2nd days after infection.

There was a transient increase in the stores of cardiac glycogen on the 5th day after infection.

Glycogen stores of voluntary muscle were significantly reduced on the 5th and 6th days after infection. It is thought that this depletion resulted from a reduction in muscular activity rather than from an impairment of glycogenesis.

Suppression of P. berghei infections but not those of N. rodhaini or T. brucei in mice on milk diet were noted. The suppression of P. berghei was variable. This was not due to differences of the quality of the milk or to the mice eating faeces, sawdust, etc. which may be rich in PABA. The variability was at least partially due to selection of a strain of parasite probably requiring a lower level of PABA than normal. One such strain was isolated and its pattern of infection compared with the normal strain. The ‘milk diet’ strain caused a higher fatality rate in mice on milk diet but always showed a lower parasitaemia growth rate in mice on normal diet. When repassaged through mice on normal diet, the ‘milk diet’ strain did not revert immediately to the infection pattern of the normal strain.

Infective Haemonchus contortus cayugensis larvae were stimulated to exsheath in 0·02 m-Na2B4O7. 10H2O, into which was bubbled CO2. The larvae under the exsheathing stimulus were found to be coiled and sluggish. The larvae became very active after most of the CO2 was removed by compressed air, oxygen or nitrogen. The exsheathment rate in each of the latter instances was higher than when larvae were exsheathed completely in an atmosphere of CO2. Carbon dioxide is an essential component of the exsheathing stimulus, but the continued presence of a high pCO2 or carbonic reaction products appeared to inhibit larval motility and caused lower exsheathment rates.

Further investigations have been carried out on the nature of ‘host’ antigens associated with the adult worms of Schistosoma mansoni. These investigations show:

1. The ‘host’ antigens are not removed from the surface of the worms by thorough washing and prolonged incubation in Hanks's balanced salts solution. The antigens must be firmly bound or even incorporated at the surface.

2. Monkeys cannot be immunized against ‘mouse worms’ with mouse IgG immunoglobulins. Accordingly it is unlikely that the ‘host’ antigens are mouse anti-worm antibodies.

3. The ‘host’ antigens are certainly associated with the membranes of mouse erythrocytes. They may also be associated with the ‘soluble protein’ fraction of the erythrocytes.

4. Immunization with sheep erythrocytes failed to protect monkeys against challenge with ‘mouse’ worms. Therefore it is unlikely that the ‘host’ antigens are Forssman antigen.

5. The mouse ‘host’ antigens associated with ‘mouse’ worms are not major histocompatibility antigens. Consequently it is likely that they are species-specific mouse antigens.

Infective Haemonchus contortus cayugensis larvae were stimulated to exsheath in 0·02 m-Na2B4O7. 10H2O saturated with varying concentrations of CO2. Larvae stimulated to exsheath with 40% CO2 gave a higher exsheathment rate than larvae stimulated with 99·95 % CO2. There was a linear relationship between the exsheathment rate and the shaking rate over the range from 40 to 100 c/min when the larvae were stimulated to exsheath with 99·95 % CO2.

The course of the worm burdens of calves infected daily with larvae of Ostertagia ostertagi at five different rates was studied by making post-mortem worm counts on groups of calves killed after experiencing infection for different periods of time.

The relationship between worm numbers and infection rates together with evidence that a turnover of worms occurred, led to the conclusion that burdens of adult worms were regulated primarily by a loss of worms at a rate proportional to the number present.

Further, estimates based on the number of developing fourth-stage larvae indicated that the proportion of the larvae administered which became established decreased gradually as the experiment progressed.

At very low infection rates, the rate of turnover of the worms was slower than at high infection rates but in all groups it remained constant through the 6 months duration of the experiment.

The development of a small proportion of the larvae administered was arrested at the early fourth stage. At the highest infection rate used, the proportion of worms that became inhibited was somewhat greater.

Adult S. mansoni from a recently infected rhesus monkey (Macaca mulatta) were transferred into the hepatic portal systems of a normal rhesus and of a rhesus which had acquired complete resistance to the parasite. The worms were recovered after 2 days and examined by light and electron microscopy.

The worms recovered from the normal monkey were undamaged. Most of the worms recovered from the hyperimmune monkey were alive but had localized aggregations of host cells on their surfaces. Small areas of the tegument of these worms showed structural and degenerative changes, namely an increase in density and vacuolation of the tegument; the formation of small, round, membrane-bounded cytoplasmic bodies within vacuoles in the tegument; the breakdown of the outer membrane of the tegument and release of the cytoplasmic contents; and finally the complete disappearance of the tegument exposing the underlying muscle fibres. Host monocytes and polymorphonuclear leucocytes were closely applied to severely damaged parts of the tegument; the host cells appeared to be phagocytic. The other tissues of the worms were normal. Apparently the above damage is a result of the host's immune reaction which is directed against the tegument of the worms. Worms grown in mice and subsequently transferred to monkeys immunized against mouse antigens are similarly damaged, but in this case the damage occurs more rapidly.

Infective Haemonchus contortus cayugensis larvae were harvested from faecal cultures, cleaned and stored at 4°C. By means of small sample runs, exsheathment rates were determined for batches of clean larvae prior to and during storage. The larvae were stimulated to exsheath at 40°C in 0·02 m-Na2B4O7. 10H2O into which a gas mixture of 40% CO2–60% N2 was bubbled. A 20 and 60 min exsheathing time produced some and no decrease in exsheathment rates respectively for freshly cleaned unstored larvae and larvae stored 1–12 weeks. In all instances there was a reduction in the exsheathment rate 24 h after the larvae were placed in cold storage. This was considered a result of a cold shock from which the larvae did not recover until after the fourth day.

Various endocrine operations were performed on the adult female cockroach Blatta orientalis and the adult populations of the nematode Hammerschmidtiella diesingi were recorded 2 or 4 weeks later. Cautery of the median neurosecretory cells (m.n.c.) caused a significant reduction in total numbers of adult nematodes after 2 or 4 weeks; after 2 weeks, removal of the retrocerebral complex (corpora cardiaca plus corpora allata) caused a significant overall reduction in the adult nematode burden and this could not be prevented by reimplanting the corpora allata immediately after the retrocerebral complex had been removed.

Anomalies appeared in the data when the sex of the parasite was examined and this may be related to a possible postembryonic mode of sex determination.

Both m.n.c. cautery and removal of the retrocerebral complex suppressed host terminal oocyte development and ootheca production, whilst reimplantation of corpora allata into ‘retrocerebralectomized’ cockroaches allowed reproductive processes to continue normally. Hence, the m.n.c. and corpora allata are essential for host egg development.

Histological studies showed a profound reduction in fuchsinophilic material in the corpora cardiaca of m.n.c. cauterized cockroaches.

Although the m.n.c. may affect the nematode directly or indirectly, a direct effect on the parasite by the corpora allata is unlikely.

The distribution of N. brasiliensis within the small intestine of rats, following a primary infection, is described.

The fourth stage larvae were found to inhabit the sections later parasitized by the adult population.

Both the larval and adult worms were found to be confined to the anterior half of the small intestine. This aggregation is believed to be under the influence of stimuli (factor(s) 1), present in the lumen of the host gut.

The adult worms also clumped within the already confined worm population. This behaviour is thought to be due to intrinsic behaviour patterns of the worm, sexual attraction and thigmokinesis.

Larval and adult worms were surgically transferred to points, at varying distance from the ‘normally’ inhabited region, in the small intestine of fresh recipient rats. The resulting migratory behaviour of the worms was studied.

The worm populations resulting from both the larval and the adult transfers showed the ability to recognize that they were in the wrong position of the small intestine and to be able to orientate, migrate and locate the ‘normal’ site.

Infective Haemonchus contortus cayugensis larvae were rapidly exsheathed (20 min) using 0·02 m-Na2B4O7. 10H2O, a gas mixture of 40 % CO2–60 % N2, and subsequent aeration with compressed air as reported previously. Several variables in this system were examined. The optimum concentration of sodium tetraborate was found to be 0·02 m. The exsheathment rate decreased with increasing molarities of the salt over the range 0·02–0·08 m. Exsheathment rates were low when the larvae received the full stimulus to exsheath for only 5 and 10 min before aeration. The larvae required at least 15 min of the full stimulus before aeration to ensure high exsheathment rates. The rapid method of ecdysis caused no abnormalities in or death of larvae, and all the larvae at the end of the incubation period were very motile and appeared normal. The exsheathment rate was consistently high as the larval concentration was increased from 2 ×103 to 2×106/10 ml of 0·02 m-Na2B4O7. 10H2O.

An adult female Polymorphus minutus releases only mature eggs into the intestine of its final host. These eggs come from the pool of eggs in the body cavity of the worm which contains only about 30% of mature eggs, the rest being immature. An analysis of the age structures of the egg populations in the body cavity and the uterus shows that an assortment of mature and immature eggs has taken place as the eggs pass from the body cavity to the uterus. The uterus contains only mature eggs and these are the eggs which are about to be released. The only pathway whereby eggs can enter the uterus from the body cavity is through the uterine bell. This suggests that it is the uterine bell which is able to select mature eggs from the mixture of eggs in the body cavity.

A uterine bell in vitro engages in precisely patterned muscular activity which propels eggs through its branching lumen. In one part of the bell (the grooves between the median wall cells and the lappets of the uterine duct cells), the patterned muscular activity passes mature eggs into the uterus and immature eggs back into the body cavity to complete their development. The greater length of mature eggs seems to be the character which enables them to be ‘recognized‘ by the uterine bell.

Owl monkeys infected with the Malayan Camp strain of Plasmodium falciparum were found to have malarial antigens in their serum at the height of infection. The antigens were identical with certain malarial S-antigens present in the sera of West African (Gambian) children acutely infected with P. falciparum. The infected owl monkey thus appears to provide an experimental model which is relevant to the study of the serology of human malaria.

A description is given of the morphology and behaviour of the oncomiracidium of the monogenean D. sagittata. The larva has many features in common with the oncomiracidium of Diplozoon paradoxum but its development is less precocious than the latter. Suggestions are made as to the possible relationships of a pair of degenerate hooks on the haptor.