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SUMMARYEggs of chicken ascarids (Ascaridia galliandHeterakisspp.) are believed to be hardy and survive for long periods. However, this has not been evaluated quantitatively and our study therefore aimed to determine development and recovery of chicken ascarid eggs after burying in pasture soil. Unembryonated eggs were mixed with soil, placed in sealed nylon bags and buried at 7 cm depth in pasture plots April (spring,n= 72) and December 2014 (winter,n= 72). Eight randomly selected bags per season were used to estimate pre-burial egg recovery [0 week post-burial (wpb)]. Eight random bags were removed at 5, 12, 23, 38, 52, 71 wpb per season and additionally at 104 wpb for spring burial. The content of each bag was analysed for numbers and development stages of eggs. Eggs buried in spring were fully embryonated within 12 wpb. In contrast, eggs buried in winter were developing between 23 and 38 wpb, so that all viable eggs seemed to be fully developed by 38 wpb. About 90% eggs disappeared within 23 wpb (spring) and 38 wpb (winter). Small proportions (2–3%) of seemingly viable and infective eggs were still recovered up to 2 years after deposition. In conclusion, most eggs buried in temperate pasture soil seem to experience a heavy mortality within a few months after the deposition, especially during warm periods. However, a small proportion of eggs may survive and remain infective for at least 2 years.

SUMMARYSusceptability of Ascaridia galli to benzimidazole (BZ) was investigated using faecal egg count reduction test (FECRT), in ovo larval development test (LDT) and genetic markers (mutations at codons 167, 198 and 200 of β-tubulin gene). Six flocks (F1−F6) of a commercial laying hen farm with different number of exposure to BZ were recruited. The FECR was calculated by analyzing individual faeces (F1, F2, F4 and F5) before and 10 days after treatment. The LDT was performed on parasite eggs from pooled samples from F1 to F6 and LC50 and LC99 were calculated. DNA was extracted from 120 worms and sequenced for β-tubulin gene. In all flocks, the FECRs were above 95% (lower CI above 90%). No significant difference was observed (p > 0·05) among obtained LC50 (F1/F4 and F2/F5 vs F3/F6) in the LDT. However, LC50 and LC99 were higher than suggested values for declaration of resistance in other nematode species. No variation was observed in codon positions involved in BZ resistance. Overall, our results indicated lack of evidence of resistance to BZ in A. galli. More research is needed to confirm these results and to further optimize the existing tools for detection and monitoring of anthelmintic resistance in A. galli.

SUMMARYThe population dynamics of Ascaridia galli was studied in 70 ISA Brown layer pullets, 42 of them were each experimentally infected with 500 embryonated A. galli eggs and 28 chickens were kept as uninfected controls. Six chickens from the infected group and 4 from the control group were necropsied at 3, 7, 10, 14, 21, 28 and 42 days post-infection (d.p.i.). The mean worm recovery varied from 11–20% of the infection dose with the highest recovery at 3 d.p.i. and the lowest at 21 and 42 d.p.i. (P P P

This study compared the prevalence and intensity of infections of helminths in 2 chicken breeds in Vietnam, the indigenous Ri and the exotic Luong Phuong. Also, possible correlations with the Major Histocompatibility Complex (MHC) were tested. The most prevalent helminths wereAscaridia galli,Heterakis beramporia,Tetrameres mothedai,Capillaria obsignata,Raillietina echinobothridaandRaillietina tetragona. Differences in prevalence and intensity of infection were found between the 2 breeds. Comparing the 2 groups of adult birds, Ri chickens were observed to have higher prevalence and infection intensities of several species of helminths, as well as a higher mean number of helminth species. In contrast,A. galliandC. obsignatawere shown to be more prevalent in Luong Phuong chickens. Furthermore, an age-dependent difference was indicated in the group of Ri chickens in which the prevalence and the intensity of infection was higher for the adult than the young chickens for most helminths. The most notable exception was the significantly lower prevalence and intensities ofA. galliin the group of adult chickens. In contrast, the prevalence and intensity were very similar in both age groups of Luong Phuong chickens. Using a genetic marker located in the MHC, a statistically significant correlation between several MHC haplotypes and the infection intensity of different helminth species was inferred. This is the first report of an association of MHC haplotype with the intensity of parasite infections in chickens.

SUMMARYAcquired resistance against Ascaridia galli infection was studied in seventy-two 18-week-old white Leghorn chickens allocated to six groups (G1–G6). In order to understand the population dynamics following trickle-infection (100 eggs per chicken twice weekly), chickens of subgroups of G1 were necropsied 3 days after 1, 6 or 12 inoculations (G1A, G1B and G1C respectively), while G2–G4 were inoculated for 6 weeks. G2 was necropsied 4 weeks after the last inoculation. The number of established larvae increased initially (between G1A and G1B) but decreased after repeated inoculations (G1C, G2). G3, G4 and G5 were used to measure the efficacy of anthelminthic treatment and to monitor the acquisition of resistance following a challenge infection. At week 7 G3, G4 and G5 were treated with flubendazole for 7 days in the feed. Two weeks after treatment the chickens in G4 and G5 were challenged with 500 eggs. G6 was left as uninfected control. Necropsy at week 10 after first inoculation revealed a lower establishment rate, an impaired development and a more posterior localization of the larvae in G4 (trickle-infected-treated-challenged) compared with G5 (treated-challenged). IgY level in serum reached noticeable level at 14 dpi in G2 and G4 chickens, and in G4 chickens IgY level further increased after challenge infection. The study provides evidence that acquired resistance against A. galli in chickens leads to a significant yet incomplete protection against re-infection.

SUMMARYThe metabolism of 5-hydroxytryptamine (5-HT), octopamine (OA) and dopamine (DA) by adult male Ascaridia galli was investigated by incubating worms cut into 5 mm lengths with radio-isotope labelled amine. [14C]5-hydroxytryptamine and [14C]octopamine were taken up by the tissues and were metabolized to apolar products that co-chromatographed using both high-performance liquid chromatography and thin-layer chromatography with N-acetyl 5-hydroxytryptamine (NA5-HT) and N-acetyloctopamine (NAOA), respectively. N-acetylation was by far the most important reaction detected under these experimental conditions. A brief incubation of cut worms with [3H]dopamine resulted in the formation of a radio-isotope labelled metabolite that co-chromatographed with N-acetyldopamine (NADA) on reversed-phase high-performance liquid chromatography. The N-acetyltransferase activity towards 5-hydroxytryptamine and octopamine was detected in crude homogenates of male worms only when the co-substrate, acetyl CoA, was added to the reaction mixture. This enzyme activity appeared to be mainly localized in a 40 000 g supernatant fraction. The failure of previous studies to detect N-acetylation of biogenic amines in tissue homogenates of nematodes may have been due to the low levels of acetyl CoA present in these enzyme preparations.

AF3 (AVPGVLRFamide) and AF4 (GDVPGVLRFamide) are endogenous RFamide-like peptides isolated from the parasitic nematode Ascaris suum. Here the actions of these peptides on the somatic musculature of Ascaris have been investigated and compared to the action of acetylcholine (ACh), the excitatory transmitter at the neuromuscular junction. ACh, AF3 and AF4 contracted muscle with EC50s of 13±1 μM, 24±6 nM and 37±2 nM, respectively (n=6). The muscle cells were depolarized by ACh (3 μM; 5·2±0·4 mV, n=42), AF3 (1 μM; 2·6±0·3 mV, n=19) and AF4 (1 μM; 3·3±0·4 mV, n=19). EC50s were 681±329 nM (AF3) and 901±229 nM (AF4), but an estimate could not be made for ACh due to muscle contraction at concentrations greater than 10 μM. The depolarization to 3 μM ACh was abolished by the nicotinic receptor antagonist mecamylamine (10 μM; n=5) but the responses to the peptides were not (111±7% and 108±17% with respect to control; n=5). The depolarization elicited by ACh was reduced to a greater extent by a 50% reduction in extracellular Na+ concentration than the response to AF3 and AF4 (PAscaris muscle without an action at the Ascaris nicotinic receptor. Furthermore, the ionic mechanism through which AF3 and AF4 depolarize Ascaris muscle is different from that for ACh. ACh, AF3 and AF4 were also found to contract Ascaridia galli somatic muscle with EC50s of 13±3 μM, 721±236 nM and 371±177 nM, respectively (n=7). The muscle cells were depolarized by ACh (EC50=14±5 μM, n=5), AF3 (EC50=5±3 μM, n=4) and AF4 (EC50=10±5 μM, n=4). Therefore the response to these peptides is not unique to Ascaris and they may subserve a functional role in the motor nervous system of parasitic nematodes.

SUMMARYVasoactive intestinal polypeptide (VIP)-Hke protein was detected by dot blot analysis in the excretions/secretions (E/S) of Nematodirus battus and Ascaridia galli and was confirmed in the E/S of Nippostrongylus brasiliensis. ELISA analysis showed that N. brasiliensis E/S contained the highest proportion of VIP-like protein (28·04 pmoles/mg of total E/S protein) and A. galli E/S contained the lowest (10·89 pmoles/mg of total E/S protein). Peptide histidine isoleucine (PHI)- like protein was detected by dot blot analysis in the E/S products of N. brasiliensis, N. battus and A. galli. ELISA analysis suggested that A. galli E/S contained the highest proportion of PHI (20·77 nmoles/mg of total E/S protein) and N. battus E/S contained the lowest (0·67 nmoles/mg of total E/S protein). The possible significance of VIP-like and PHI-like substances in the E/S of gastrointestinal nematodes is discussed.

SUMMARYEvidence for the presence of adipokinetic hormone/hypertrehalosaemic hormone (AKH/HrTH)-like peptides in the parasitic nematodesAscaridia galliandAscaris suumhas been obtained using insect bioassays which measure hyperglycaemic responses to peptides belonging to the AKH/HrTH family of insect hormones. A peptide fraction extracted from heads and tails ofAscaridia gallievoked a dose-dependent hyperglycaemic response when injected into the cockroach,Periplaneta americana. Maximal bioactivity was obtained with material that was equivalent to 38 mg (wet weight) of nematode. Bioactivity appeared to be highest in extracts from heads and tails of both male and female worms and could be fractionated into at least three peaks of hyperglycaemic activity by reversed-phase high-performance liquid chromatography. An extract from heads and tails ofA. suumalso evoked a hyperglycaemic response when injected into the cockroach,Blaberus discoidalis. The bioactivity was inactivated on incubation with pure endopeptidase 24.11, confirming the peptidic nature of the bioactive material. These results provide evidence for the existence of peptides related to the insect AKH/HrTH family of peptides in parasitic nematodes.

Cytochemical staining with diaminobenzidine (DAB) has been used to locate cytochrome oxidase activity in mitochondria from major tissues of three intestinal parasitic nematodes, Nippostrongylus brasiliensis, Haemonchus contortus and Ascaridia galli. Deposition of DAB reaction product was uniform and relatively intense in mitochondria from all tissues studied in N. brasiliensis. However, mitochondria from different tissues of H. contortus and A. galli varied considerably in their cytochemical staining, decreasing in the order hypodermis < muscle < gut < reproductive tissue. Mitochondria in gut and reproductive tissue of A. galli possessed little or no cytochrome oxidase activity. These results are compatible with respect to oxygen availability and the extent and localization of the mammalian-type aerobic mitochondrial electron transport pathway in intestinal parasitic nematodes.

SUMMARYThe effect of continuing ingestion of eggs of A. galli on growth rates of chickens placed on different nutritional levels was studied under repeated doses of 10, 100 and 1000 infective eggs/day. With increasing amounts of protein in feed, there occurred significant weight differences between infected groups, the highest protein levels showing the longest duration in weight depression due to infection. On the other hand, assuming adequate nutrition of host, highest effects on growth rates were seen in chickens receiving daily doses of 1000 eggs daily and the lowest in chickens receiving 10 eggs daily.The effect of repeated dose on growth rate is similar to the effect of single infections reported by previous workers except that the duration of the growth depression was much longer in the former due to pathogenic effects of inhibited larvae.The author is indebted to the Department of Technical Cooperation, under whose Fellowship this study was carried out; to the Department of Zoology, Edinburgh University, where the work was done; to the Ministry of Agriculture, Fisheries and Food; Poultry Research Laboratories, Lasswade, for the free supply of chickens used here; and finally to Dr J. A. Campbell of Edinburgh University for his keen interest and advice throughout this work.

SUMMARYThe pathogenicity and pathology of Ascaridia galli infections of poultry were studied using repeated doses of varying numbers of eggs. No significant effect due to infection was seen on p.c.v. and Hb. values of infected chickens. Haemo concentration occurred parallel with sporadic diarrhoea, which follows high levels of repeated dosing. This phenomenon complicated the interpretation of blood protein values. A/G ratios were, however, worked out and analysed. No significant differences were noticed between the groups and it was concluded that under the levels of inoculation employed during the study there were no significant effects of A. galli infections on blood protein values as well as p.c.v. and Hb.values of infected chickens.Symptomatic developments, macroscopic lesions and pathological changes of intestinal tissues due to infection were followed up in detail. They were most severe in chickens on the least nutritive diet and sustaining the highest levels of repeated doses. Pathogenicity of larval and adult parasites was described. The presence of large numbers of adult parasites was associated with intestinal obstruction in host. This was seen mostly in chickens on low nutrition and sustaining either low or high levels of repeated inoculation, and very rarely also in chickens under high plane of nutrition but sustaining repeated inoculation of small numbers of eggs. Cellular infiltration as a result of infection was found to be extremely rare.It was present as fibroblasts and only in association with dead larvae.The author is indebted to the Department of Technical Cooperation, under whose Fellowship the study was carried out; the Department of Zoology, Edinburgh University, for facilities provided; the Ministry of Agriculture, Fisheries and Food; Lasswode Poultry Research Laboratories, for the free supply of chickens used here; Dr J. A. Campbell of Edinburgh University for his keen interest, encouragement and advice throughout this work; and finally to G. Obiwelozor for reproducing the photographs from the original manuscript.

1. Studies were made on the morphology, with special emphasis on the taxonomic characters, of 220 mature male and female Ascaridia lineata (Schneider) from chickens at Manhattan, Kansas, U.S.A., and Cambridge, England.2. Eggs arising in the anterior ovary pass into the posterior uterus; similarly, eggs from the posterior ovary pass into the anterior uterus.3. In young females eggs may be fertilised at any place in the uteri; in adults, fertilisation occurs near the distal ends of the uteri.4. With the aid of a micromanipulator, a small structure in one pole of the mature egg, previously decribed as an opening, an opercular plug in the shell, or as an internal thickening of the shell, was found to be a solid, conical appendage of the vitelline membrane, free from the shell.5. Fertilised eggs develop to the coiled embryo (infective) stage in 16 days when incubated in water at 30° C.; in 1 mm. of water at 33° C., they become infective in 10 days.6. Water cultures of fertile eggs do not develop when kept at constant temperatures of 0° C., or of 10° C.; at 15° C., development proceeds.7. Constant refrigeration of fertile eggs in water cultures for 1 month at 0° C. so lower the vitality that, on being incubated subsequently at 30° C., they divide slowly and soon die; keeping the eggs at 10° C. for 1 month has no deleterious effect on them when incubated subsequently at 30° C.8. In hatching, the embryo may escape from any part of the egg shell, either in the duodenum of the host, or in water cultures; newly hatched larvae swallowed by the chicken seldom become established; infestation normally result from the ingestion of embryonated eggs.9. The habitat of A. lineata is the duodenum, especially the portion which is a few centimetres posterior to the entrance of the bile ducts; determination of hydrogen-ion concentrations showed that the nematodes live in nearly neutral media (av. 6·7).10. Penetration of the duodenal mucosa by larvae 10–17 days old is frequent in young chickens; occasionally, a larva goes on through the intestinal wall to the liver and lungs, but ordinarily, after the 17th day the young worms withdraw from the mucosa into the lumen of the intestine.11. Young A. lineata grew to maturity in 50 days in chickens parasitised when about a month old; in six 8-day periods following hatching of the larvae, the average daily growth in length per period was about 0·12 mm. in the first period, 0·75 mm. in the second, 1·5 mm. in the third, fourth, and fifth periods, and 3mm. in the sixth period.12. At least three moults occur before the adult from of the nematode is developed. Important morphological changes associated with the moults include: after first moult, presence of pre-anal swelling (males), and of anal prominence in both sexes; after second moult, lips with oral papillae and dentigerous ridges, projecting Iateral folds (alae) present in newly hatched larvae replaced by non-projecting lateral lines, females with vulva and shorter tail proportionately, and males with pre-anal sucker and three pairs of caudal papillae; after third moult, external characters similar to those of the adult A. lineata.

1. Qo2 values for Haemonchus contortus egs varied between − 9·7 and − 12·6 according to the degree of development of the embryos. The r.q. was in the region of 0·6.2. Young infective larvae of Nippostrongylus muris had a high Qo2 (−18·4), which fell as the larvae aged. Third stage Haemonchus contortus larvae gave similar results. The respiration was not affected by exsheathment.3. Adult parasites gave Qo2 values as follows: Ascaridia galli, − 2·5; Nematodirus spp., − 5·1; Nippostrongylus muris, − 6·8; Neoaplectana glaseri, − 12·6. When calculated on a surface area basis, Ascaridia galli had an oxygen uptake which was much higher than that of the other organisms.4. Qco2 values were small. The r.q. of infective larvae, which contain fat as reserve material, was about 0·72. The other forms which contained much glycogen as well as fat had r.q. values between 0·6 and 0·7. A. galli was an exception in that an r.q. of about 0·95 was obtained.5. Potassium cyanide inhibited respiration in all the forms examined.The author is indebted to Dr R. W. Glaser for supplying a strain of Neoaplectana glaseri.

The electrophysiological properties of the bag region of the somatic muscle cells of Ascaris suum and Ascaridia galli were studied using intracellular techniques. For Ascaris muscle cells, the mean resting membrane potentials at 20 and 37°C were −29·9 and −33·8 mV respectively, and the average input conductance was 2·12 μS. For the muscle cells of A. galli similar values were obtained. For example, the mean input conductance of these cells was 2·84 μS at 20°C. Healthy Ascaris muscle cells at near physiological temperatures show both spontaneous depolarizing and hyperpolarizing activity and, in cells close to the nerve cords, rhythmic large amplitude (approximately 30 mV) action potentials are observed. Such action potentials, which are very sensitive to temperature variations, originate in the muscle cells. In contrast the muscle cells of Ascaridia are quiescent. The rhythmic action potentials of Ascaris are resistant to tetrodotoxin (TTX) (≤ 10−6 M), verapamil (10−4 M) and cinnarizine (10−4 M), but are blocked irreversibly by 22, 23 dihydroavermectin B1a (10−7 to 5 × 10−6 M). GABA, and the GABAA receptor agonists, muscimol and isoguvacine, hyperpolarize and increase the input conductance of both Ascaris and Ascaridia muscle cells. The antagonists+bicuculline and picrotoxin were not effective in modulating the spontaneous hyper polarizations of Ascaris muscle cells, and picrotoxin (10−4 M) was not effective in altering the response to GABA (5 × 10−6 M). The significance of the results is discussed briefly.

SUMMARYThe population dynamics of Ascaridia galli infections of poultry was studied under repeated doses of 10, 100 and 1000 eggs. Daily doses were continued for 6 weeks only. At low dose rates patency is noted by the fifth week. At higher dose rates there is an accumulation of larvae whose development has been arrested at a precise developmental stage, i.e. the third larval stage. Sporadic development of some of these larvae to adults occurs later. Arguments are produced to show that this inhibition of larval development is a resistance and not a density-dependent phenomenon. The epidemiological significance of this inhibition is discussed. This resistance phenomenon is shown to occur in single infection experiments where 1000 eggs were used. This gives rise to the development of a worm population of two facies. The whole finding is suggested to be related in some way to the phenomenon of ‘tissue phase’, which is accepted as a normal life-cycle behaviour of this parasite. A brief review of previous work on this is given and it is postulated that the ‘tissue phase’ phenomenon is not an obligatory part of the normal life-cycle of the parasite but represents a reaction to factors of resistance inherent in chickens and controlled to a large extent by a complex dynamic interplay of dose size and the chickens.I wish to thank the Department of Technical Co-operation and the Federal Government of Nigeria for financing this project, Dr Boulton of the Poultry Research Centre, Edinburgh, for advice on nutrition, and the Department of Zoology, especially Dr J. A. Campbell, University of Edinburgh, for facilities and advice on the work. I am greatly indebted to the Ministry of Agriculture, Fisheries and Food, Poultry Research Laboratories, Lasswade, for the free supply of chickens used in this work.

1. The r.q. of wholeNeoaplectana glaserirose from 0·56 to 1·10 when glucose was added to the medium. TheQo2was only slightly affected. Respiration of other nematode parasites was largely unaffected by exogenous glucose. Pyruvate had little or no effect.2. Inorganic phosphate increased whenAscaris lumbricoidesmuscle brei was incubated. In the presence of fluoride, or when aqueous extracts were used, easily and difficultly hydrolysable phosphate was formed. Phosphatase activity was dominant even in aqueous extracts ofA. lumbricoidesintestinal tissues and fluoride inhibited Poformation only slightly. Ptot., and PresIdualfell markedly in wholeA. lumbricoideswhich had been incubated anaerobically. Under aerobic conditions Pofell slightly, but the other components rose considerably. Phosphorylative activity ofA. lumbricoidesovary was greater than in the muscle. Phosphorus compounds in perienteric fluid did not change during incubation.3. The breakdown of glycogen and the formation of glucose in aqueous extracts ofAscaridia galliwas inhibited by fluoride and phloridzin. Polysaccharide was synthesized in fluoride-poisoned preparations when glucose 1-phosphate was added. Polysaccharide formation inAscaris lumbricoidesfluoridepoisoned muscle preparations was demonstrated without the addition of Cori ester.4. Fructose 1:6-diphosphate added to aqueous extracts ofAscaridia galliandNematodirusspp. was rapidly metabolized at pH 6·5. At pH 7·2 the fructose content increased.5. In aqueous extracts ofNematodirusorAscaridiabrei which had been autolysed for short periods, 55–60% of the glycogen utilized appeared as glucose. Only small amounts of lactate were formed. Aqueous extracts ofNematodirusandAscaridiabrei which had been autolysed for long periods formed glucose in excess of the glycogen disappearing. When perienteric fluid, which contained amylase, was removed fromA. gallibefore autolysis, the amount of glucose formed was very much reduced. It is suggested that the excess glucose was formed from dextrins which were not estimated as glycogen and which were hydrolysed by perienteric fluid amylase during incubation.Lactate decreased during the incubation of extracts prepared from brei which had been autolysed for long periods.6. Bicarbonate decreased during the anaerobic incubation of aqueous extracts ofNematodirusspp. andAscaridia galliwhich were buffered with CO2-bicarbonate. The decrease in bicarbonate was in excess of the CO2expelled from the medium by acid formation.7. The acid-soluble phosphorus compounds of the different tissues ofAscaris lumbricoideswere examined. Compounds similar to a.t.p. were found in the intestine, ovary, muscle and possibly also in the perienteric fluid. The acid-unstable phosphorus compounds did not appear to be either creatine- or arginine-phosphate. Compounds similar to Embden ester were found in the ovary and muscle. The occurrence of the phosphate compounds found in the parasite is compared with figures given for other organisms.8. It is concluded that carbohydrate fermentation as far as lactate in nematode parasites was similar to that found in yeast and mammalian muscle. Energy was transferred by means of high-energy phosphate bonds.9. Phospholipids, which were found in considerable amounts in the tissues ofA. lumbricoides, were estimated as lecithin, sphingomyelin and serine- and ethanolamine-containing phospholipids. The amounts of the phospholipids found in the parasite tissues are compared with figures given for other organisms.The authors are deeply indebted to Prof. D. Keilin and Dr T. Mann of the Molteno Institute, Cambridge, for their advice and critical reading of the manuscript. Thanks are also due to Dr E. F. Gale and Dr E. Friedemann for advice on analytical procedures.

A tissue phase of the nematode A. dissimilis has been demonstrated. The larvae enter the tissue soon after hatching and not, as previously thought, after 7 days.The growth rate of A. dissimilis in young poults has been studied. Sexual differentiation can be observed from the 14th day and sexual maturity occurs as early as 28 days after infection.From the recorded figures it is evident that A. dissimilis is not necessarily a smaller species than A. galli. The age of the host influences the development of maturity of the worms and probably the size of the nematodes as well. The largest female recorded here was 128 mm and the largest male was 77 mm when removed from a turkey 76 days after infection.The infectivity of A. dissimilis ova is not impaired after storage at room temperature in 1 % formalin for up to 237 days. Embryonation is complete in 9–10 days at 30 °C.It has been shown that chickens are probably refractory to A. dissimilis.We wish to acknowledge the technical assistance of Mr J. Brownbill, Mrs B. Fisher and Mr P. R. Mills.

1. Compared with the mammalian intestine, uterus and blood serum, the corresponding organs and perienteric fluid ofAscaris lumbricoideswere found to have a high phosphorus content. The muscle of the parasite, however, contained little more than half the phosphorus found in the mammalian muscle.2.A. lumbricoidestook up inorganic ortho-phosphate largely or exclusively through the alimentary tract. Small amounts were taken up by the cuticle and the lateral line system, but did not appear to pass on to other tissues.3.Nippostrongylus murisin the intestine of the rat took up radioactive phosphorus which had been injected into the host intramuscularly. When the host was dosedper osthe radioactivity appeared in the parasites at a lower concentration than in the host's small intestine.4.Ascaridia gallifailed to show any radio-activity when host birds were injected intravenously with inorganic orthophosphate containing P32. A sudden rise and fall in the radioactivity of the parasites were found when host birds were dosedper os.5. It is suggested that nematode parasites have a high demand for phosphate which they take up largelyper os. Ascaridia gallifeeds rapidly, but with poor phosphate absorption, on host gut contents.Nippostrongylus murisfeeds on host tissues. It is suggested that the different feeding habits ofN. murisandAscaridia gallimay have some relation to the efficacy of anthelmintics against these parasites.The authors are indebted to Dr M. Kamen and Dr E. Reinhard of Washington University, St Louis, for a gift of radioactive phosphorus. Thanks are also due to Mr E. Parrish and Mr L. Turk of the McMaster Laboratory for their capable assistance.