Treatment of mice infected with S. mansoni by various sterilants effective against male rodents produced phases of inhibition of schistosome oviposition assessed by miracidial counts. In the treated worms, besides apparent disappearance of the testes, marked involution of ovarian tissue occurred. The gonads of both male and female worms seem to be directly affected by the antifertility substances. It is suggested that gamete production in both sexes follows similar lines in contrast to the finite reservoir of meiotic oocytes in mammals.

The relationship between the ciliated epidermal cells and the subepidermal layer of the miracidium of Fasciola hepatica has been described. Non-ciliated ridge-like extensions of the subepidermal layer separate the ciliated epidermal cells from each other. The sunken portions of the subepidermal layer, each containing a nucleus, lie below the outer body wall muscles of the miracidium and open into the ridge by narrow neck-like connexions. Elongate vesicles, which may be a source of stored plasma membrane similar to that which occurs in the transitional epithelium of other animals, fill most of the ridge. In addition, characteristic round electron dense granules are found in the ridge but the majority are found in the sunken portions of the subepidermal layer.

The development and origins of the tegument of the sporocyst of F. hepatica have been described at the ultrastructural level. When the miracidium is in the process of penetrating the snail host, large vacuoles appear between the ciliated epidermal cells and the basal lamina which overlies the muscles of the body wall. These vacuoles have the effect of loosening the epidermal cells from the basal lamina of the body wall of the miracidium. Possible mechanisms involved in the formation of such vacuoles are suggested and discussed.

During penetration of the snail the ciliated epidermal cells of the miracidium are lost; the ridge, a syncytial layer between the epidermal cells which is connected with the subepidermal layer, spreads over the basal lamina and exposed body wall muscles of the metamorphosing sporocyst to form the new outer covering of the sporocyst.

Cytoplasm passes from the subtegumentary layer into the tegument during this stage of the development of the body wall of the sporocyst. Muscular contraction and microtubules may be involved in the outward movements of this cytoplasm. The nuclei of the subtegumentary layer remain below the muscles of the body wall.

Twenty-four hours after penetration of the snail the outer plasma membrane of the tegument forms folds, which greatly increase the surface area.

Sixty hours after penetration involutions between the folds, which may indicate pinocytosis, are present, and it is suggested that pinocytosis may play a role in food absorption.

The fully formed tegument is a syncytial layer containing numerous electron dense granules, vacuoles, mitochondria and lipid droplets.

The results on the formation of the tegument of the sporocyst have been discussed with reference to the controversy about the origins and terminology of the outer covering of the Platyhelminths.

It has been shown that in common with other malarial species the drug response in the sporogonous cycle of Plasmodium cynomolgi parallels in a special way the drug response in the schizogonous cycle. Thus, prophylactic drugs produce deteriorating changes in the oocysts while curative drugs have a destructive effect on the sporozoites. A comparison of the effects of prophylactic drugs on the sporogonous and schizogonous cycles of the four malarial species studied thus far suggests the presence of more than one pre-erythrocytic developmental stage in the schizogonous cycles of P. vivax and P. cynomolgi following the initial invasion by the sporozoite.

Eggs of T. colubriformis and H. contortus were separated from faeces. Their response to desiccation was compared by subjecting them, at different stages of development, to a range of relative humidities. Many eggs of T. colubriformis at all stages of development survived desiccation at relative humidities down to 75%, whereas the only H. contortus eggs to survive were those exposed to the highest relative humidity and which had already undergone a substantial amount of development before desiccation.

It has been shown that in samples of the eggs of T. colubriformis, the smaller eggs (i) have a greater probability of survival when incubated at fixed temperature and saturation deficit; (ii) require less time to develop and hatch when incubated in water at constant temperature, and (iii) have a greater surface area relative to volume, than do the larger eggs.

A hypothetical basis for the relation between egg size and desiccation survival is briefly discussed.

1. The distribution of filarial larvae in the dorsoventral and dorsal-longitudinal muscle fibre groups was studied in serial sections of mosquitoes of a susceptible strain of Aedes aegypti infected with Brugia pahangi or subperiodic B. malayi and of wild-caught Mansonia uniformis mosquitoes containing the latter parasite.

2. The experiments showed that more larvae were situated in the dorsal-longitudinal muscle than in the dorsoventral and that the difference in numbers was highly significant.

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.

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.

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.

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.

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.

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.

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.

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.

In the uninfected hepatopancreas of L. truncatula 7·0–11·0% of the dry weight is lipid. Of the total lipid 60% is neutral lipid and 40% is phospholipid. Free fatty acid is the major neutral lipid component; triglycerides, diglycerides, monoglycerides, sterols and esterified sterols are also present. The phospholipids identified were phosphatidyl choline, phosphatidyl ethanolamine, lyso-phosphatidyl choline and sphingomyelin. The fatty acids were analysed by gas chromatography. The major fatty acid is C16 (palmitic) and 60% of the total fatty acids are saturated.

In the hepatopancreas of L. truncatula infected with the rediae of F. hepatica, but with the rediae removed, 5·4–9·4% of the dry weight is lipid. Of this total lipid 73% is neutral lipid and 27% is phospholipid. All the fractions of neutral lipid, except the fatty acids are smaller than in the uninfected hepatopancreas. The fatty acids show an increase of 38%. The same phospholipids identified in the uninfected hepatopancreas are present, but all the fractions show a decrease in amount with the exception of the phosphatidyl choline fraction, which is present in approximately equal amounts in both the uninfected and the infected hepatopancreas. The major fatty acid is palmitic acid.

A typical postparturient rise of parasite egg output occurred in a group of lactating ewes. At parturition these animals carried few inhibited fourth-stage larvae and the rise was associated with a net increase in parasite populations, which did not occur in non-lactating ewes. Lactating ewes whose established parasite populations were effectively removed just prior to parturition showed a similar rise derived entirely from infection acquired during lactation, which was of much greater magnitude than that seen in similarly treated non-lactating animals. Circumstantial evidence of increased fecundity of T. colubriformis females in lactating ewes was also obtained.

It was concluded that the postparturient rise of egg output may derive from an increase in adult parasite populations by an increased rate of establishment of newly ingested infective larvae which develop to the adult stage without inhibition, as well as by the resumption of development of previously inhibited fourth-stage larvae. In addition, both newly acquired and established adult female parasites may show increased fecundity.

Ewes whose lambs were removed at birth or after a period of lactation showed a rapid fall in faecal egg counts associated with rejection of part of their existing worm burden and a pronounced increase in resistance to new infection.

All of the differences observed between lactating and non-lactating ewes in the behaviour of their parasite populations were found to be qualitatively the same as those that have been frequently reported in susceptible and resistant non-reproductive sheep. The hypothesis is suggested, therefore, that the postparturient rise derives from a pronounced but temporary relaxation of immunological control of gastro-intestinal nematode infection associated with the endocrine status of the lactating ewe.

A method is described for producing unisexual infections of N. brasiliensis in rats; this method was used primarily to obtain populations of virgin adult females. Experiments were carried out in which male worms were introduced to virgin females in the rat small intestine. The worms were recovered after periods varying from 30 min to 22 h and the females were examined for fertile egg production or other evidence of insemination.

In some experiments a few females were inseminated within 30 min of being mixed with males, but for reliable results a period of over 1 h was necessary. Sperm were first deposited along the ventral wall of the vagina and there was evidence that a single insemination could fill the vagina. After 4·5 h the majority of females had been inseminated and this period was long enough for sperm to reach the seminal receptacle in one female. A minority of females had a few fertile eggs in the uterus by 5·5 h, and fertile eggs were being passed by 6·0 h after the introduction of males.

Small numbers of males were introduced to an excess of virgin females in order to obtain information on the sexual capacity of males. These experiments indicated that males could, on average, fertilize one female every 2 h during the first 15–20 h. This potential was shown to be greatly in excess of the minimum requirements for maintaining the maximum fertile egg output of females in normal infections.

An intestinal trematode of shrews previously identified as Opisthioglyphe locellus Kossack, 1910, by Macy & Moore (1958) in Oregon is identified as Neoglyphe soricis (= Opisthioglyphe soricis) originally described from Sorex araneus L., in Poland by Pojmańska (1956). N. soricis found in Sorex cinereus, near Anchorage, Alaska, is a new host and new locality record. N. soricis, the only species of Neoglyphe known from North America, is compared with its Eurasian counterpart and closely related species. Evidence supporting the retention of the genus Neoglyphe originally proposed as a subgenus by Shaldybin (1953), and raised to generic rank by Yamaguti (1958), and invalidated by Zarnowski (1960), is presented.