Showing papers in "Parasitology in 1973"
TL;DR: A comparison with young, but not inseminated worms, suggests that the presence of sperm in the oviduct is not the major stimulus which induces maturation of the female worm.
Abstract: The ultrastructure of the reproductive system of mature (54-day-old), immature (32-day-old) and females from unisexual infections of Schistosoma mansoni is described in detail. The uterus is tegumentary in structure but the vitelline duct and oviduct are complex and possess cilia as well as lamellae on their luminal surfaces. The characteristics of the cells forming the walls of the ducts suggests that they may have a digestive function. The posterior portion of the oviduct of the adult worm contains sperm which become enveloped by lamellae. The vitelline cells of the adult contain vitelline droplets, much lipid and little glycogen. A second type of body derived from endoplasmic whorls is also present. Mehlis's gland contains only one type of gland cell and these cells pass through the ootype wall and open into its lumen. The female from unisexual infections has an incompletely developed Mehlis's gland, an ovary in which the Golgi complexes do not produce typical cortical granules and has vitelline cells which remain immature. The oviduct, ootype and uterus are well developed in contrast to the vitelline duct.
A comparison with young, but not inseminated worms, suggests that the presence of sperm in the oviduct is not the major stimulus which induces maturation of the female worm.
193 citations
TL;DR: The semi-defined medium contains an acid hydrolysate of casein : in the empirically devised defined medium the casein requirement has been circumvented by inclusion of additional vitamins and amino acids, which are very hypertonic.
Abstract: Semi-defined and defined media for the growth of culture forms of Trypanosoma brucei sspp. have been developed by enrichment of tissue culture medium 199 with additional vitamins, amino acids, salts and other compounds. The semi-defined medium contains an acid hydrolysate of casein: in the empirically devised defined medium the casein requirement has been circumvented by inclusion of additional vitamins and amino acids. Both media are very hypertonic. Control of pH was found to be particularly critical for growth. The optimum temperature for growth in the semidefined medium was between 25°C and 28°C, but cells would undergo one or two division cycles at 37°C.
182 citations
TL;DR: Ultramicroscopic features of the ookinete/oocyst transformation in Plasmodium berghei are described and spindles at different phases of division were observed with kinetochores in early and late anaphase position.
Abstract: Ultramicroscopic features of the ookinete/oocyst transformation in Plasmodium berghei are described. The apical complex of organelles and some pellicular components, believed to be responsible respectively for cell penetration and body form were resorbed into the cytoplasm shortly after the ookinete came to rest under the basal lamina of the midgut wall. Within a single digitate nucleus, spindles at different phases of division were observed with kinetochores in early and late anaphase position. From the number of kinetochores the chromosome complement was estimated at 5–10.
131 citations
TL;DR: In this article, daily infection with doses of approximately five oocysts of Eimeria tenella produced an infection with an extended patency which ceased by the time the birds had received about 140 oocyst.
Abstract: Daily infection with doses of approximately five oocysts of Eimeria tenella produced an infection with an extended patency which ceased by the time the birds had received about 140 oocysts. Total oocyst production was comparable with that in birds given the same number of oocysts in a single dose, but the immunity to subsequent heavy challenge was significantly greater. Continuous exposure to low-level infections may be more comparable to the field situation and the present results suggest how birds can acquire a strong immunity without showing evidence of clinical disease.
88 citations
TL;DR: It is suggested that although T. suis may not be an important pathogen in its own right, its activities in the caecal and colonic mucosa may cause sufficient damage to enable secondary pathogenic invaders to become established.
Abstract: The biology of the life-cycle of Trichuris suis of the pig is described and discussed together with aspects of the hosi-parasite relationship. Development of the infective L. 1 larval stage within the egg was shown to be influenced by temperature. Following ingestion of infective ova by the pig, all subsequent larval development to the adult stage occurred in the mucosa of the caecum and colon. Eggs hatched in the distal region of the small intestine and throughout the large intestine. Larvae then penetrated the caecum and colonic mucosa via the crypts of Lieberkuhn, where they entered the cells lining the crypts.
The ensuing histotrophic phase lasted 13 days, during which time a gradual larval migration occurred from the deeper regions of the lamina propria to areas immediately beneath the surface mucosal epithelium. Luminal development was initially seen on day 16 when the posterior extremities of larvae were protruded into the gut lumen; from day 20 the entire posterior body region was exposed, while only the filamentous anterior region of the parasite remained embedded in the mucosal surface. The prepatent period varied from 41 to 47 days.
Four moults were observed during development within the host and these occurred on days 10, 16, 20, 32 and 37 (to form the L. 2, L. 3, L. 4 and L. 5 or adult stage respectively).
It is suggested that although T. suis may not be an important pathogen in its own right, its activities in the caecal and colonic mucosa may cause sufficient damage to enable secondary pathogenic invaders to become established.
84 citations
82 citations
TL;DR: In this paper, a cross-cross between two lines of Plasmodium berghei yoelii differing in drug-sensitivity and enzyme type was made between mice.
Abstract: Crosses have been made between two lines of Plasmodium berghei yoelii differing in drug-sensitivity and enzyme-type. The two lines used were line A, which is pyrimethamine-resistant and contains an electrophoretic form of glucose phosphate isomerase termed GPI-1, and line C, which is pyrimethamine-sensitive and contains enzyme-form GPI-2.
Equal numbers of blood forms of lines A and C were mixed and injected intravenously into a mouse. Mosquitoes were fed immediately on the mixture, and the resulting sporozoites used to infect further rodents. After treating these animals with pyrimethamine, drug-resistant parasites characterized by GPI-2 could be detected in the remaining infections. Controls showed that these parasites were recombinant forms, which had arisen by cross-fertilization of gametes in the mosquitoes, and not by mutation or ‘synpholia’.
By cloning the products of crosses between lines A and C by dilution, parasite lines of two recombinant classes (resistant GPI-2 and. sensitive GPI-1) were isolated, together with lines of parental characteristics.
75 citations
TL;DR: The immune reaction of larvae of D. algonquin against P. bochei was characterized either by the melanization and encapsulation of the parasites or by the production of melanized particles.
Abstract: The immune reaction of larvae of D. algonquin against P. bochei was characterized either by the melanization and encapsulation of the parasites or by the production of melanized particles. In successful host reactions the eggs of the parasite were killed before they were completely melanized and encapsulated by haemocytes. When host larvae were transferred during the early stages of infection to a diet that contained phenylthiourea (PTU), the incidence of melanization and encapsulation of the parasites was significantly reduced. However, if the hosts were transferred to the diet just before the eggs of the parasite were normally melanized, PTU had virtually no inhibitory effect, and the immune reaction rate remained very high. These results suggest that the biochemical reactions associated with melanization constitute an important part of the immune reaction of D. algonquin. The data provide additional evidence to support the idea advanced by other workers that the phenoloxidase system plays an important role in insect immunity against some internal metazoan parasites. It is suggested that, during infection, the phenoloxidase system of the haemocytes is activated by hormonal imbalance.
72 citations
TL;DR: Larvae, which had emerged from their eggs at some time between 20 and 80 min previously, responded to host skin, suggesting that an initial uninfective period is of short duration or absent, and there is a strong endogenous component to the rhythm.
Abstract: When the eggs of the skin parasitic monogenean Entobdella soleae are subjected in the laboratory to alternating periods of light and darkness (LD 12:12, LD 6:18 or LD 18:6) at constant temperature (selected from the range 12–16 °C), hatching is rhythmical, most of the oncomiracidia emerging during the first 4 h of the period of illumination on each successive day.Rhythmicity in response to alternating 12 h periods of light and darkness persists in a wide range of lighting conditions including natural daylight and in dim blue light, the latter being similar in intensity (65 nW/cm2) and in spectral quality to light at the depths where the host Solea solea lives.The hatching rhythm persists with a periodicity of about 24 h in constant darkness and in constant light, provided that the eggs have been exposed previously to LD 12:12 until hatching begins. This indicates that there is a strong endogenous component to the rhythm.Eggs laid and maintained in total darkness develop and hatch, but the oncomiracidia may emerge at any time during each 24 h period and there is little evidence of rhythmicity.When alternate 12 h periods of light and darkness are reversed after the commencement of hatching, the hatching pattern also reverses after 24 h, so that emergence of larvae occurs at the beginning of the new illumination period.Mechanical disturbance plays little or no part as a hatching stimulus.Larvae, which had emerged from their eggs at some time between 20 and 80 min previously, responded to host skin, suggesting that an initial uninfective period is of short duration or absent.Hatching soon after dawn may have high survival value for E. soleae in view of the host's activity pattern; soles are active at night and partly bury themselves in the sediment (where the eggs of the parasite lie) at dawn, and the fish is inactive and a stationary target during the day.
67 citations
TL;DR: In this paper, a functional abomasal lesion was apparent within 4 days of infection judged by the changes in plasma pepsinogen levels and the sodium concentrations of the pouches contents.
Abstract: Sheep in which abomasal fundic pouches had been made were infected with Ostertagia circumcincta (150000 larvae in one sheep, 100000 in three sheep). Subsequently studies were made on pouch secretion, food intake, plasma pepsinogens and abomasal pouch secretory responses when the sheep first ate. A functional abomasal lesion was apparent within 4 days of infection judged by the changes in plasma pepsinogen levels and the sodium concentrations of abomasal contents.
Whereas the secretory activity of the abomasal fundic pouches (never exposed to parasites) was maintained or increased, the pH and sodium concentration of contents taken from the infected part of the abomasum were indicative of either a failure to secrete or of a permeability reabsorptive lesion. Ultrastructural studies demonstrated that parietal cells of the pouches had the appearance of cells subjected to strong secretory stimuli, but those of infected abomasa were similar to cells of gastric mucosa subjected to agents suppressing secretion.
Factors which might operate, on the one hand, to stimulate secretion from separated fundic abomasal pouches, and on the other to inhibit or modify the secretory activity of the fundic mucosa of the infected abomasa, are discussed.
66 citations
TL;DR: The histology and ultrastructure of the salivary gland in Dermacentor andersoni are presented with particular emphasis on those aspects relating to fluid secretion in this article, and it is suggested that the group III acinus contributes most of the fluid portion of the saliva (i.e. water and small molecules) and that the main cell type involved is what we name the water-cell.
Abstract: The histology and ultrastructure of the salivary gland in Dermacentor andersoni are presented with particular emphasis on those aspects relating to fluid secretion.
We suggest that the group III acinus contributes most of the fluid portion of the saliva (i.e. water and small molecules) and that the main cell-type involved is what we name the ‘water-cell’.
The granule-cells possibly secrete the cement by which the tick secures its mouthparts to the host, and the ‘vacuolar cell’ possibly produces a protein-rich secretion. The function of the group I acinus remains obscure.
TL;DR: Juvenile hormone and its analogues inhibited growth of Panagrellus redivivus and of the free-living stages of Haemonchus contortus.
Abstract: Juvenile hormone and its analogues inhibited growth of Panagrellus redivivus and of the free-living stages of Haemonchus contortus. Substances extracted from nematodes had similar actions and also showed the activity of juvenile hormone in insects. Partly purified material from 1 g of freezedried juveniles of H. contortus contained about 200 Tenebrio units.
TL;DR: The life-cycle of Lobatostoma manteri is the simplest two-host cycle of trematodes known and must be considered the most primitive one, of a type from which digenean life-cycles have evolved.
Abstract: Lobatostoma manteri sp.nov. is described. It differs from other species of this genus in the number of marginal alveoli (usually 56–62), the location of the testis near the posterior end and the large size of the cirrus pouch. Mature worms occur in the intestine of the fish Trachinotus blochi. Eggs containing fully developed larvae are laid. The eggs are eaten by snails and hatch in the stomach. Larvae have an oral sucker, pharynx, simple caecum, ventro-terminal acetabulum, two dorsal excretory bladder cells in front of the acetabulum, and a caudal appendage. They migrate into the digestive gland and differentiate to pre-adults with fully developed genital organs and the full number of alveoli on the adhesive disk; young spermatozoa and egg cells develop but do not mature. Pre-adults have a minimum number of 8500 sensory papillae on the surface. The worms are usually found in a cavity formed by enlargement of the main duct and one or more (?) side ducts of the digestive gland near the stomach in Cerithium moniliferum, or in the stomach and main ducts of the digestive gland of Peristernia australiensis. They may creep from the ducts into the stomach and back into the ducts. Fish become infected by eating snails. Worms from fish die soon after transfer into sea water but can be kept alive for up to 13 days in frog's Ringer solution or dilute sea water (1:5), in which they lay eggs containing larvae infective to snails. Worms from snails remain alive in sea water, dilute sea water, frog's Ringer or Tyrode solution. Eggs of worms from single infections have the haploid chromosome number of 7; there is normally no self-fertilization and development does not reach the blastula stage. The life-cycle of Lobatostoma manteri is the simplest two-host cycle of trematodes known. Reasons are given why it must be considered the most primitive one, of a type from which digenean life-cycles have evolved.
TL;DR: Experiments in wild field mice and laboratory-bred wild house mice showed that the parasite elicited an immune response similar to that previously described in strains of laboratory mice, and it is suggested that in these mice pregnancy and/or lactation may have suppressed the immune response, allowing the accumulation of a worm burden in excess of the threshold for worm expulsion.
Abstract: The results of experimental infections of Trichuris muris in wild field mice (Apodemus sylvaticus) and laboratory-bred wild house mice (Mus musculus) showed that the parasite elicited an immune response similar to that previously described in strains of laboratory mice. Experiments in laboratory mice showed that the parasite was able to become sexually mature only when small single infections or repeated low-level infections were given. A survey of a population of 43 wild house mice naturally infected with T. muris showed that the pattern of small worm burdens in the majority of mice was consistent with a situation of repeated low-level infection, except in the case of six female mice which harboured larger mature worm burdens. It is suggested that in these mice pregnancy and/or lactation may have suppressed the immune response, allowing the accumulation of a worm burden in excess of the threshold for worm expulsion.
TL;DR: Cattle injected with supernatant fluids from ticks fed for 4–9 days became infected, and this could be correlated with the histological detection of mature parasites in the corresponding ticks.
Abstract: Rhipicephalus appendiculatus ticks, infected with Theileria parva , were fed on rabbits and removed at daily intervals for 9 days. Half of the ticks removed were dissected and their salivary glands processed and examined for parasites. The remaining ticks which had been removed were ground up and aliquots of the supernatant fluid thus obtained were injected into East Coast fever susceptible cattle. Cattle injected with supernatant fluids from ticks fed for 4–9 days became infected, and this could be correlated with the histological detection of mature parasites in the corresponding ticks. The most highly infective supernatant fluids were prepared from 5-day-fed ticks. In a second experiment it was shown that female ticks of a variety of weights contained infective particles of T. parva .
TL;DR: In this article, the chemical constituents of tissue fluid and serum in rabbits infected with trypanosoma (Trypanozoon) brucei, as compared with uninfected, control animals, were made.
Abstract: Perforated plastic cylinders (hair curlers) were implanted subcutaneously in rabbits for the collection of tissue fluid. Using this technique, a study was made of the chemical constituents of tissue fluid and serum in rabbits infected with Trypanosoma (Trypanozoon) brucei, as compared with uninfected, control animals. Changes were caused by the infection in the concentrations of proteins, electrolytes, urea, creatinine, cholesterol and pyruvate, and in the activities of the enzymes aspartate transaminase, creatine phosphokinase and alkaline phosphatase.
Antitrypanosomal antibody, detectable by the indirect fluorescent antibody technique, was shown to penetrate the tissue fluid and to reach a titre of about one-fifth of that in the serum. Renal failure, probably resulting from allergic reactions, was shown to be a contributory cause of death in rabbits infected with T. (T.) brucei.
TL;DR: The egg and larval stages of Trichuris suis can be briefly characterized as follows: the egg: barrel shaped, possesses a thick shell consisting of three thick outer layers and an inner thin vitelline membrane, is unsegmented and unfertilized when freshly deposited.
Abstract: The egg and larval stages of Trichuris suis can be briefly characterized as follows:
The egg: barrel shaped, possesses a thick shell consisting of three thick outer layers and an inner thin vitelline membrane, is operculate at each end and is unsegmented and unfertilized when freshly deposited.
L. 1 within the egg: presence of an oral spear, a poorly denned oesophagus and an intestinal tract consisting of undifferentiated granulated material.
L. 1 within the host: initial differentiation of an oesophagus, cell body, intestine and rectum.
L. 2: further differentiation of the body organs and the appearance of the rudiments of the reproductive system.
L. 3: initial development of reproductive system and development of a cloaca in the male thus distinguishing the sexes.
L. 4: differentiation of reproductive system into vagina, uterus, oviduct and ovary in the female, and testis, vas deferens, ejaculatory duct, spicule and spicular muscle, sheath and tube in the male.
L. 5 or adult stage: completed development of the sexual organs including formation of the vulval orifice and eggs in the female and seminal vesicle in the male.
TL;DR: It is suggested that standard curves for normal infection rate — reproductive potential relationships under strictly specified conditions may be of value in choosing appropriate infection rates for critical experimental work to assess the effects of anticoccidial compounds on oocyst production.
Abstract: Experiments using chicks of specified strain, age and sex raised under identical conditions on the same diet and infected with known strains of coccidia are described. The relationships between the infection rates and resulting oocyst productions of Eimeria acervulina and E. tenella are presented graphically and are used to demonstrate a crowding effect. Possible contributory factors to the crowding effect and possible reasons for the differences between the E. acervulina oocyst production of unmedicated birds or birds medicated with decoquinate are discussed. It is suggested that standard curves for normal infection rate — reproductive potential relationships under strictly specified conditions may be of value in choosing appropriate infection rates for critical experimental work to assess the effects of anticoccidial compounds on oocyst production.
TL;DR: The capsule is exclusively, or almost exclusively, formed from and by the infected muscle fibre, as might be concluded from the presence of the sarcolemmal basal lamina surrounding the capsule substance during the initial stages of capsule formation.
Abstract: The encapsulation of Trichinella spiralis larvae in host striated muscle was studied.Capsule formation starts at 13 days post-infection. Between days 20–50 p.i. the largest increase in capsule formation was observed. The capsule is exclusively, or almost exclusively, formed from and by the infected muscle fibre, as might be concluded from the presence of the sarcolemmal basal lamina surrounding the capsule substance during the initial stages of capsule formation. A collagen nature of the capsule cannot be excluded.
TL;DR: In this paper, mouse peritoneal macrophage cells suspended in a TC 199 calf serum medium and cultured in Leighton tubes, were infected with Trypanosoma (Schizotrypanum) cruzi culture forms in order to study the development of this parasite in vitro.
Abstract: Mouse peritoneal macrophage cells suspended in a TC 199 calf serum medium and cultured in Leighton tubes, were infected with Trypanosoma (Schizotrypanum) cruzi culture forms in order to study the development of this parasite in vitro. Three cycles of development were thought to occur:
1. Epimastigotes or trypomastigotes were taken up by macrophages and transformed into amastigotes. These multiplied by binary fission and ruptured the infected cell after 4‐5 days. Released amastigotes were taken up by uninfected macrophages and the cycle was repeated.
2. A small proportion of intracellular amastigotes developed into ‘ovoid forms’ which transformed progressively into promastigotes, epimastigotes and trypomastigotes.
3. Some amastigotes became ‘round forms’ from which sphaeromastigotes developed. These transformed directly into trypomastigotes without the formation of epimastigotes.
TL;DR: These findings, with the known similarity of the life-cycle stages, pathogenicity and pathology, indicate that E. mivati is not sufficiently different from E. acervulina to be a distinct species.
Abstract: Two strains each of Eimeria acervulina and Eimeria mivati were examined for their ability to develop in the chorioallantoic membrane (CAM) of chicken embryos and the caeca of chickens. It was found that between 100 and 1000 times more sporozoites of E. acervulina were needed to produce infections in the caeca and the embryo CAM respectively. The reproduction of both species in infections of chickens was similar and a high degree of cross-protection occurred.It was found that oocysts of E. mivati differed in size and shape depending upon whether they were produced from infections of embryos or chickens. When maintained by passage in chickens they assumed size and shape characteristics of E. acervulina.These findings, with the known similarity of the life-cycle stages, pathogenicity and pathology, indicate that E. mivati is not sufficiently different from E. acervulina to be a distinct species. It is suggested that it is best referred to as E. acervulina var. mivati.
TL;DR: The structure and development of the spermatozoon of Dipetalonema viteae has been studied by means of electron microscopy and complex membraneous organelles are suggested to have similar origins and functions to the acrosome of the typical mammalian spermatoZoon.
Abstract: The structure and development of the spermatozoon of Dipetalonema viteae has been studied by means of electron microscopy.
Spermatogonia are developed from a syncytium in the terminal region of the reproductive tract. The syncytium grows along the length of the testis as an anucleate rachis, carrying with it the developing germ cells. The gametes become detached from the rachis when they have become secondary spermatocytes. The chromosomes which appear in the primary spermatocytes at the onset of meiosis persist throughout all subsequent stages of development. The nucleus is not reconstructed. Cytophores are produced by the spermatids at the end of the second meiotic division. The spermatid is an elongated cell, but the mature spermatozoon, within the male tract, is amoeboid. There are only minor differences between the sperm found in the male and female tracts. The male gametes contain complex membraneous organelles which are developed from the Golgi bodies and endoplasmic reticulum of the primary spermatocytes. These organelles are suggested to have similar origins and functions to the acrosome of the typical mammalian spermatozoon.
TL;DR: The results indicate that self-cure of H. contortus infections under natural conditions occurs in the absence of reinfection and is apparently non-immunological in origin.
Abstract: The phenomenon of self-cure, as it occurred under field conditions in East Africa, was studied in Merino sheep infected with Haemonchus contortus. The onset of self-cure, as judged by a dramatic fall in faecal egg counts, was found to be simultaneous in sheep grazing on infected pasture and in sheep grazing on parasite-free pasture. Furthermore the results of autopsies carried out before and after self-cure showed that a marked and equal loss of adult worm burdens had also occurred. These results indicate that self-cure of H. contortus infections under natural conditions occurs in the absence of reinfection and is apparently non-immunological in origin. Since the phenomenon was always associated with a period of significant rainfall, it is suggested that new growth of pasture may be a significant aetiological factor.
TL;DR: In this article, it was shown that in a single chronically infected animal there are numerous different antigenic populations of trypanosomes each occupying separate brain sites and a hypothesis to account for this antigenic diversity is given.
Abstract: Trypanosomes were isolated before and after the formation of infected detectable antibody from various brain sites and the blood of Microtus montanus. All isolates were serotyped by the agglutination reaction, and the isolates obtained prior to antibody formation were serologically identical to the original inoculum. Later isolates obtained from separate sites of an infected animal were serologically different from the original inoculum and also from each other. It was therefore concluded that in a single chronically infected animal there are numerous different antigenic populations of trypanosomes each occupying separate brain sites. A hypothesis to account for this antigenic diversity is given.
TL;DR: The effect of oxyclozanide (2,2′-dihydroxy-3,3′,5,5′,6-pentachlorobenzanilide) on Hymenolepis microstoma in the bile duct of mice and H. diminuta in the small intestine of rats was measured as discussed by the authors.
Abstract: The effect of oxyclozanide (2,2′-dihydroxy-3,3′,5,5′,6-pentachlorobenzanilide) on Hymenolepis microstoma in the bile duct of mice, and H. diminuta in the small intestine of mice and rats was measured.
Oxyclozanide at doses as low as 4mg/kg removed 13-day-old H. diminuta and caused no obvious harmful effect to the rat host up to the maximum level (256 mg/kg) tested. Worms were displaced and degenerating within 1 h. Results in mice were more difficult to assess because of the immune response, but similar total amounts of oxyclozanide caused destrobilation and loss of 7-day-old H. diminuta.
Oxyclozanide was less effective against 21-day-old H. microstoma attached in the bile duct. Approximately half the strobila was lost following dosing at 5 mg/kg and progressively greater amounts as the dose level was increased. At 50 mg/kg worm loss commenced but even at 150 mg/kg 25 % of worms survived. The time taken to regrow to the original adult size varied but was complete within 7–9 days at levels up to 25 mg/kg. Double dosing at 5-day intervals did not enhance the effect of a single dose. The apparent existence of a sensitivity gradient down the strobila in H. microstoma is discussed.
TL;DR: Lipid levels of infective larvae of Ancylostoma tubaeforme are reduced and their behavioural activity declines with age, and behavioural activity using the percentage active, rate of activity, and the percentage of larvae able to penetrate a membrane is measured.
Abstract: Lipid levels of infective larvae of Ancylostoma tubaeforme are reduced and their behavioural activity declines with age. We have measured behavioural activity using the percentage active, rate of activity, and the percentage of larvae able to penetrate a membrane. Neostigmine bromide, a cholinergic drug, increased larval activity in all tests. Larvae, stored at 4 and 10 °C and in hypertonic saline, were inactive but consumed lipid. When returned to isotonic saline at 26 °C, these larvae were no more active than those at 26 °C throughout. We found no evidence that such inactive larvae had entered a state of quiescence. All our results, and those of other workers, have been used to emphasize that larval ageing is related directly to decreased metabolic rates, and not primarily to lipid levels.