Fine structure of trophozoites of the gregarine Leidyana ephestiae (Apicomplexa: Eugregarinida) parasitic in Ephestia kuehniella larvae (Lepidoptera)

The ultrastructure of the eugregarine Leidyana ephestiae, parasitic in the larval gut of the flour moth, Ephestia kuehniella, is described. Guts of experimentally infected larvae of E. kuehniella were fixed and sectioned for electron microscope studies of young and mature trophozoites. Young unsegmented trophozoites were small, oval to ovoid, and possessed a simple, globular epimerite. The plasma membrane covering the epimerite region was continuous with the plasma membrane of the protodeutomerite and was in close contact with that of the host cell. Three cortical membranes covered the protodeutomerite region. Folding of the protodeutomeritic epicyte occurred after about 2 days of development of the gregarine. After 3–4 days the body of the trophozoite became differentiated into three segments. A septum was visible between protomerite and deutomerite, but there was nothing similar to this structure between epimerite and protomerite. Fully developed trophozoites showed a large ovoid epimerite containing many mitochondria and vesicles. The epimerite was situated on a short neck filled with fibrils. The cytoplasm of protomerite and deutomerite was rich in amylopectin granules and electron-dense bodies.     

Leidyana canadensis N. Sp. (Apicomplexa: Eugregarinida) from Larval Eastern Hemlock Looper, Lambdina fiscellaria fiscellaria (Lepidoptera: Geometridae)

ABSTRACT. Leidyana canadensis n. sp. (Apicomplexa: Eugregarinida) is described from larvae of the eastern hemlock looper, Lambdina fiscellaria (Lepidoptera: Geometridae) collected near St. Stephen, Charlotte County, New Brunswick, Canada. Gamonts solitary, located between host ventricular peritrophic membrane and ventricular epithelium. Protomerite very broadly ellipsoid with transverse posterior margin; length 43.7 μm, width 42.7 μm; protomerite-deutomerite septum strongly constricted. Deutomerite narrowly obovoid with anterior transverse margin; length 186.6 μm, width 58.7 μm; total length 227.1 μm. Nucleus spherical to broadly ellipsoid; length 26.3 μm, width 20.2 μm; placement abaxial in the posterior 2/3 of the deutomerite. Nucleus often obscured in late gamonts. Association late, caudofrontal, ephemeral and leading directly to syzygy. Gametocysts roughly spherical; diameter 216.7 μm; hyaline coat increasing diameter to 359.1 μm. Gametocysts mature and dehisce through six short spore tubes within 48 hours. Oocysts axially symmetric, dolioform in dorsal aspect, compressed in the plane perpendicular to the major axis, very uniform in size and shape; length along major axis 5.2 μm, terminal width 1.8 μm, medial width 3.8 μm; extruded in chains.     

Two New Menosporine Gregarines, Hoplorhynchus acanthatholius N. Sp. and Steganorhynchus dunwoodyi N. G., N. Sp. (Apicomplexa: Eugregarinorida: Actinocephalidae) from Coenagrionid Damselflies (Odonata: Zygoptera)

ABSTRACT. Hoplorhynchus acanthatholius , n. sp. is described from Enallagma civile , the Civil Bluet damselfly. Trophozoites are solitary, lie in the mesenteron between the peritrophic membrane and the epithelium, and attain a maximum length of 850 μm. Epimerite ovoid to broadly ovoid; anterior margin bearing eight equidistant retroarcuate hooks; attached to protomerite by means of a vermicular stalk. Protomerite ovoid; deutomerite narrowly obvoid. Gametocysts spherical; diam 300 μm, sporulating by simple dehiscence in 48–72 h. Oocysts are characteristic of Menosporinae: smooth, biconical, crcscentic, uniform in size and shape. Steganorhynchus dunwoodyi , n. g., n. sp. is described from the damselfly Ischnura verticalis. The genus is characterized by an epimerite comprising an ovoid papilla enclosed in a retractable, globular sheath, borne on a long vermicular stalk. Trophozoites are solitary, lie in the mesenteron between the peritrophic membrane and epithelium, and attain a maximum length of 605 μm. Protomerite very broadly ovoid; deutomerite obvoid. Gametocysts spherical; diam 258 μm, sporulating by simple dehiscence in 48–72 h. Oocysts are characteristic of Menosporinae: smooth, biconical, crescentic, uniform in size and shape. The population dynamics of H. acanthatholius and S. dunwoodyi among damselfly populations in five Nebraska localities are presented.     

Gregarina coronata N. Sp. (Apicomplexa: Eugregarinida) Described from Adults of the Southern Corn Rootworm, Diabrotica undecimpunctata howardi (Coleoptera: Chrysomelidae)

ABSTRACT. Gregarina coronata n. sp. (Apicomplexa: Eugregarinida) is described from the adults of the Southern Corn Root Worm, Diabrotica undecimpunctata howardi (Coleoptera: Chrysomelidae). Measurements given are means, in micrometers, taken from mature gamonts in association. Primite: protomerite hemi-ellipsoidal with basal tumidus, length 47.6, width 44.0, with cytoplasmic granule, apical crown apparent; deutomerite elongate ellipsoidal, length 227.9, width 81.3; epimerite absorbed into anterior in gamont, globular in trophozoite. Satellite: protomerite hemi-ellipsoidal, truncated at association interface to appear trapezoidal, length 39.2, width 49.6, with cytoplasmic granule; deutomerite elongate ellipsoidal, length 240.6, width 80.2; epimerite absorbed into anterior in gamont. Association caudofrontal and often precocious, occurring during growth of trophozoites. Gametocysts spherical, 115.3 in diameter, 132.9 with hyaline coat; producing multiple oocyst chains under moist storage in 24–36 h. Oocysts very uniform in shape and size, dorsad: doliform, length 6.4, equatorial width 3.4, polar width 2.9; pleuron: dorso-ventrally flattened, corpus concave with bicondylic termina; corpus height 0.98, width 4.44; terminus height 1.96, width 0.98.     

Studies on the Early Development of the Eugregarine Gregarina garnhami

SYNOPSIS. The Eugregarine Gregarina garnhami is parasitic in the mid-intestine and caecae of the desert locust Schistocerra gregaria (Forsk). The penetration oi the sporozoite and its development into a three-segmented cephalont is described. At no time in its development is the Fregarine completely intracellular; the so-called intracellular stages of other workers are shown to be the breakdoan products of the intestinal host cells themselves.
After penetrating the host intestinal cell the sporozoite grows rapidly and the anterior intracellular region outgrows the posterior estracellular region. Once the intracellular region reaches a size 13–16 μ in diameter. growth oi this region ceases and growth is now concentrated in the posterior region. When this latter region has reached 20 μ in diameter an annulus appears. This, by growing diametrically across the posterior epimerite region, divides the extracellular region into protomerite and deutomerite.
Detachment of the cephalont is considered to be a passive and not an active process and is dependent on the breakdown and extrusion of host cells. In this process the epimerite may or may not become detached from the protomerite.
A system of lonpitudinal fibres (myonemes) exists within the protomerite, and these play an important role in converting the protomerite into an adhesil-e disc prior to conjugation.
Extensive folding of the epicyte occurs in both the protomerite and deutomerite in the three-segmented cephalont; this folding could not be observed prior to the division of the gregarine into three regions. The epimerite has a dual function in the early stages of development, serving both as an attachment organelle and as an absorptive region across which iood materials may pass from the host cell.     

Eugregarine trophozoite detachment from the host epithelium via epimerite retraction: Fiction or fact?

Eugregarines represent a diverse group of Apicomplexa parasitising numerous invertebrates. Their sporozoites generally develop into epicellular trophozoites attached to the host epithelium by a specialised attachment organelle known as an epimerite. They are considered peculiar protists due to their unique cell architecture and dimensions as well as their attachment strategy which is similar to that of cryptosporidia. Using electron and fluorescence microscopy, the fine structure of the epimerite with associated structures and the mechanism of trophozoite detachment from the host epithelium were studied in Gregarina polymorpha parasitising the intestine of Tenebrio molitor larvae. The epimerite appears to be a very dynamic structure whose shape dramatically changes depending on whether or not it is embedded into the host epithelium. The trophozoite’s most fragile zone is the area below the membrane fusion site at the epimerite base. The epimerite plasma membrane forms basal radial ribs which are involved in increasing its surface and strengthening the epimerite-host cell junction. FITC-phalloidin labelling demonstrated the presence of filamentous actin in trophozoites along with its accumulation at the epimerite base and in the apical end of the protomerite, as well as a patch accumulation of filamentous actin in the protomerite of maturing and mature trophozoites. Indirect immunofluorescence revealed the presence of myosin in the cortical zone of the epimerite and in the membrane fusion site area. The data obtained strongly suggest that these structures could facilitate the detachment of a mature trophozoite from the host epithelium. Supported by data presented herein and our previous observations, we propose a new hypothesis on the mechanism of trophozoite detachment from the host epithelium based on epimerite retraction into the protomerite. This is contrary to the commonly accepted hypothesis describing gradual epimerite constriction and subsequent separation facilitated by contractility of the membrane fusion site (osmiophilic ring).     

Morphological analysis of the cellular interactions between the eugregarine Gregarina garnhami (Apicomplexa) and the epithelium of its host, the desert locust Schistocerca gregaria

Morphological features of the eugregarine Gregarina garnhami (Canning, 1956) parasitic in the caeca and mid-gut of the desert locust, Schistocerca gregaria, have been studied by transmission and scanning electron microscopy, with particular attention to the epimerite and the relationship between the epimerite and the host epithelium. The cytoplasmic core of the globular epimerite is overlain by a distinct cortical zone, limited on its cytoplasmic face by a membrane-like structure, with an underlying layer of mitochondria. The periphery of the cortical zone is strengthened by a mass of fine filaments, especially at its base. Fine tubular structures, apparently arising from the membrane-like structure, pass through the cortical zone and attach to the epimerite-host cell interface. The base of the cortical zone is supported by a distinct osmiophilic ring. The epimerite is separated from the rest of the gregarine body by a discontinuous septum. Maturing and mature trophozoites possess conically arranged fibrils, which arise from the epimeritic septum and continue into the protomerite region. The epimerite and associated structures are here discussed with regard to the detachment of the trophozoite from the host epithelium. In individuals already detached from the host epithelium, a central depression remained at the top of their protomerite, in the area formerly bearing the epimerite.     

Oviposition traps to survey eggs of Lambdina fiscellaria (Lepidoptera: Geometridae)

Outbreaks of the hemlock looper, Lambdina fiscellaria (Gueneé), are characterized by rapid increase and patchy distribution over widespread areas, which make it difficult to detect impending outbreaks. This is a major problem with this insect. Population forecasting is based on tedious and expensive egg surveys in which eggs are extracted from 1-m branches; careful observation is needed to avoid counting old unhatched eggs of previous year populations. The efficacy of artificial substrates as oviposition traps to sample hemlock looper eggs was tested as a means of improving outbreak detection and population forecasting. A white polyurethane foam substrate (1,095 lb/ft3) used with the Luminoc insect trap, a portable light trap, was highly efficient in sampling eggs of the hemlock looper. Foam strips placed on tree trunks at breast height were less efficient but easier and less expensive to use for the establishment of extensive survey networks. Estimates based on oviposition traps were highly correlated with those obtained from the 1-m branch extraction method. The oviposition trap is a standard, inexpensive, easy, and robust method that can be used by nonspecialists. This technique makes it possible to sample higher numbers of plots in widespread monitoring networks, which is crucial for improving the management of hemlock looper populations.     

Developmental polymorphism in a Newfoundland population of the hemlock looper, Lambdina fiscellaria (Lepidoptera: Geometridae)

The hemlock looper [Lambdina fiscellaria (Guenée)], a widespread and highly polyphagous Geometridae, is considered one of the most economically important defoliators of North American coniferous forests. Variations in the number of larval instars between geographic populations of this species have been previously reported in the literature. However, whether such developmental polymorphism occurs within a given population is unknown. In this study, we report the presence of both four and five larval instar individuals within a population of hemlock looper in Newfoundland when reared on balsam fir. For both sexes, the majority of individuals reared on balsam fir shoots went through four larval instars, but more than one third of the females (35.3%) went through five larval instars. Females with four larval instars developed faster and had smaller pupal weight than females with five larval instars. However, a growth-related index (weight gain per unit of time) was similar for the two ecotypes (four or five larval instars). No significant difference was observed between the two ecotypes in terms of reproductive capacity (fecundity and egg size). We also found significant differences in life history traits between males and females. Results indicate that developmental polymorphism, in this case, the variation in the number of larval instars, might provide some adaptive attributes that allowed exploitation of a broader ecological niche.     

The life cycle of Gregarina ronderosi n. sp. (Apicomplexa: Gregarinidae) in the Argentine grasshopper Dichroplus elongatus (Orthoptera: Acrididae)

Gregarina ronderosi n. sp. is described based on life cycle observations conducted on nymphs and adults of its natural host, the grasshopper Dichroplus elongatus. Following ingestion of oocysts by the host, parasite development occurs between the epithelium and the food mass in the midgut and gastric caeca. Gametocysts are liberated in the faeces. Natural prevalence in the type locality, Girondo, northwestern Buenos Aires Province, was 39.7% (n=131). The earliest trophozoites seen were small (< or = 10 microm), somewhat ovoid, unsegmented bodies. Fully developed trophozoites (the body is divided into epimerite, protomerite, and deutomerite) were slender, with conical or globular epimerites in attached or unattached forms, respectively. Trophozoites varied greatly in size [total length: 10.4-275.1 microm; mean (+/-S.E.): 126.3+/-78.9]. Gamonts, which were the most common stages observed and filled the midgut and gastric caeca in grasshoppers kept in rearing rooms, had a stocky appearance and also varied greatly in size (total length: 80-348 microm; 205+/-13). Association of gamonts was precocious, biassociative, and caudofrontal. Gametocysts were spherical and highly variable in size (96-376 microm in diameter; 202.8+/-52.5), and normally have 14 sporoduct basal discs. Everted sporoducts were up to 60 microm long. Oocysts were uniformly doliform in shape, measured (5+/-0.08 by 3.2+/-0.06 microm) and contained eight sporozoites. Wall reinforcements (carinae) were present. No infection resulted in experimentally inoculated Locusta migratoria, which is a host of Gregarina acridiorum. G. ronderosi is strikingly similar to G. acridiorum, but has larger oocysts.     

Naiadocystis phykoterion n. gen., n. sp. (Apicomplexa: Eugregarinida: Hirmocystidae), from the Mexican pygmy grasshopper, Paratettix mexicanus (Orthoptera: Tetrigidae), in the Texas big thicket with recognition of three previously described species of Naiadocystis

Naiadocystis phykoterion n. gen., n. sp. (Apicomplexa: Eugregarinida: Hirmocystidae), is described from the Mexican pygmy grasshopper, Paratettix mexicanus (Orthoptera: Tetrigidae), collected from sandbars along Harmon Creek, Walker County, Texas, in the western edge of the Texas Big Thicket. Naiadocystis n. gen. is distinguished by the form of the epimerite complex, a simple cordoid or toroid epimerite with an interior obconoid structure resembling a funnel that tapers to a distinct axial canal bisecting the protomerite, which is conspicuous in all stages of development, and a satellite protomerite reduced to a linearly crateriform cup or sucker that receives and enfolds posterior end of primite deutomerite. Association is precocious, caudofrontal, and biassociative. Gametocysts are spherical. Sporoducts are present but vestigial and irregular in number. Oocysts are broadly elliptoid with 4 small spherical polar knobs, 1 each at 30 degrees, 150 degrees, 210 degrees, and 330 degrees, and dehisce en masse. The species described herein are differentiated by their overall size and relative proportion of cellular structures. Naiadocystis acantholobae (Hoshide, 1952) n. comb., Naiadocystis acrydiinarum (Semans, 1939) n. comb., and Naiadocystis tetrigis (Corbel, 1968) n. comb. are recognized as members of Naiadocystis previously placed within Gregarina (Apicomplexa: Eugregarinida: Gregarinidae).     

Geographic biotype and host-associated local adaptation in a polyphagous species, Lambdina fiscellaria (Lepidoptera: Geometridae) feeding on balsam fir on Anticosti Island, Canada

The debate about mechanisms underlying the evolution of host specialization by herbivorous insects remains open. Natural selection may act locally and lead to different patterns of geographic variation in life history traits of polyphagous herbivores. The hypothesis of genetically-based trade-offs in offspring performance on different hosts has been proposed but this has rarely been demonstrated. Under laboratory conditions, the biological performance of two populations of the hemlock looper Lambdina fiscellaria (Guenée), a highly polyphagous lepidopteran, was compared when reared on three different tree host species: balsam fir, eastern hemlock and sugar maple. One population originated from Anticosti Island, Québec, Canada, where the insect has evolved without having access to two of the three tree species tested, the other being from the mainland where all tree species are present. When reared on balsam fir foliage, which was naturally available to each population, larvae from Anticosti Island underwent four instars compared with five for the mainland population, indicating the existence of geographic biotypes in L. fiscellaria. When reared on the foliage of non-naturally available host trees, larvae from Anticosti Island had a higher incidence of supernumerary instars. This is a unique example where local adaptation to environmental conditions of an insect herbivore is expressed through a differential number of larval instars. Moreover, the Anticosti Island population showed a higher growth related index on the host available to both populations indicating that a fitness trade-off was the evolutionary process underlying the local adaptation of this population on balsam fir.     

Epimerite-host epithelium relationships among eugregarines parasitizing the damselflies Enallagma civile and Ischnura verticalis.

The host-parasite interface between 2 species of damselflies and 4 species of eugregarines was examined at the ultrastructural level. Nubenocephalus nebraskensis organisms attached to the host midgut epithelium by means of a sucker-like protomerite; the space between the epicytic folds and host epithelium was filled with electron-dense material interpreted to be adhesive in nature. Actinocephalus carrilynnae organisms attached by means of the epimerite, which had no epicytic folds, and by the fluted stalk with characteristic epicytic folds: host cell and parasite membranes appeared fused at some places on the epimerite. Hoplorhynchus acanthatholius organisms attached by means of an ovoid epimerite with backward-pointing digitations; the entire epimerite was embedded in a host cell, and host cell microvilli surrounded the stalk. Steganorhynchus dunwoodyi organisms attached by means of an ovoid stalk papilla enclosed in a retractable globular sheath; the papilla was covered with epicytic folds, but the sheath was not, and the sheath had a single membrane, whereas the epicytic folds had 2 or 3 membranes. The entire apparatus was inserted between epithelial cells, and the sheath was highly folded at its surface. The ultrastructural observations suggest that actinocephalid gregarines have evolved 2 general strategies for attaching to the host epithelium, that is, suckerlike protomerites, as in the case of N. nebraskensis, and deeply embedded epimerites inserted within or between host cells, as in the other species studied.     

Effect of simulated fall heat waves on cold hardiness and winter survival of hemlock looper,Lambdina fiscellaria (Lepidoptera: Geometridae)

The hemlock looper (Lambdina fiscellaria) is an important pest of eastern Canadian forests. The ongoing climate warming could modify the seasonal ecology of this univoltine species that lays eggs at the end of summer and overwinters at this stage. Indeed, the increase in frequency and intensity of extreme climatic events such as fall heat waves could interfere with the winter metabolism of the hemlock looper. Moreover, the host plant quality, which influences the quantity of insect energetic reserves, the geographic origin of populations and the conditions prevailing during the cold acclimation period, could cause various responses of this pest to climate warming. The main objective of this study is to determine the impact of these factors on hemlock looper winter biology. In October 2010, hemlock looper eggs initially collected from two geographic areas in the province of Québec, and from parents reared on two host plants, were exposed to fall heat waves of different intensities during 5 consecutive days. Supercooling points and cryoprotectant levels were measured on eggs on four different dates in 2010–2011 and survival rate was measured in April 2011. Our results show that hemlock looper eggs have a very low supercooling point and high levels of trehalose, glucose and mannitol in September and November. However, there is no clear relationship between the concentration of these compounds and the decrease in supercooling points. Contents in trehalose, glucose and mannitol were significantly influenced by fall heat waves and by the origin of the population. Winter survival of eggs from the temperate population was negatively affected by strong heat waves while the boreal population was not affected. This study suggests that the metabolism and winter survival of temperate hemlock looper populations in Québec will be more affected by fall heat waves that will increase in frequency due to climate change, than boreal populations.     

Chronologie des Modifications Ultrastructurales au Cours de la Croissance de Gregarina blaberae*

SYNOPSIS. In an ultrastructural study the development of the sporozoite as well as the growth and development of the trophozoite of Gregarina blaberae were followed in the course of experimental infections of larvae of the cockroach Blaberus craniifer. The spectacular growth involved the transformation within 18 days of the sporozoite, measuring 15 × 1 μm, to a cephaline—trophozoite affixed to the intestinal epithelium—of 250 μm length and 65 μm diameter. The sporozoite's ultrastructure is not different from that of sporozoites of other Sporozoa studied to date—the conoid and dense bodies are present. The pellicle consists of 3 membranes, but there are some interruptions in the internal membrane complex. The first dictyosomes are formed from the nuclear envelope. The migration of the nucleus and of the dense bodies, followed by the regression of all the structures characteristic of the sporozoites, and the establishment of a cortical zone that comes to cover the epimerite, take place within 48 hr after infection and mark the transformation of the sporozoite into the trophozoite. Development of the cephaline involves the formation of the epicytic folds, which occurs at the base of the deutomerite, starting on the 3rd day of development. A regular system of longitudinal or epicytic folds is formed over the entire surface of the gregarine. On the 4th and 5th days of development, a vacuolar system and a chondriome become differentiated in the epimerite, while a fibrillar septum separates the protomerite from the deutomerite. The next stage, starting on the 6th day, is characterized by distribution of polysaccharide reserves between these 2 segments. The model studied allows us to determine the role of the epimerite in the parasite's nutrition, as well as the development of the chondriome and of the cortical membranes in the course of the vegetative growth phase of the cephaline gregarine.     

Short‐term influence of partial cutting on hemlock looper (Lepidoptera: Geometridae) parasitism

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Clitellocephalus americanus n. gen., n. sp. (Apicomplexa: Eugregarinida: Gregarinidae) from Cratacanthus dubius (Coleoptera: Carabidae: Harpalinae) in the Nebraska sandhills and Clitellocephalus ophoni n. comb. (Apicomplexa: Eugregarinida: Gregarinidae) from Ophonus pubescens (Coleoptera: Carabidae: Harpalinae) in Sète,France

Clitellocephalus americanus n. gen., n. sp. (Apicomplexa: Eugregarinida: Gregarinidae) is described from Cratacanthus dubius (Coleoptera: Carabidae) collected from Keith County in the Sandhills of western Nebraska. Clitellocephalus ophoni n. comb. is redescribed using original type material from Ophonus pubescens (Coleoptera: Carabidae) collected in Sète, France. Clitellocephalus n. gen. is distinguished by a deltoid epimerite with an internal anterior obconoid structure and a basal toroidal vacuole, which is retained in gamonts. Protomerites are broadly elliptical to cylindrical; deutomerites are narrowly obovate. Association is precocious, caudofrontal, and biassociative, with the satellite protomerite engulfing the posterior end of the primite deutomerite to form an interlock. Gametocysts are spherical. Sporoducts are present but reduced and irregular in number. Oocysts are dolioform, dehiscing in chains. The species described herein are differentiated by their overall size and relative proportion of cellular structures.     

Ultrastructure de la Grégarine Callynthrochlamys phronimae Frenzel; Étude Comparée de son Noyau avec Celui de Thalicola salpae (Frenzel) (Eugregarina)

SYNOPSIS. The structure of the gregarine Callynthrochlamys phronimae has been studied with the electron microscope. The cuticular complex is not different from those previously described in other species of gregarines. It is composed of 2 layers of different thickness delimited by 3 unit membranes and constitutes series of oblique folds at the surface of the deutomerite. Longitudinal rods of dense material surrounded by a slight pellicle are seen under the cuticle. Pinocytic vacuoles are present under the surface of the gregarine. Cytoplasmic organelles include mitochondria, Golgi complexes, endoplasmic reticulum, vacuoles and dense bodies from different sizes. There is a connection between the different features of the cytoplasm in the protomerite and deutomerite and the corresponding cuticular organization.
A characteristic feature of the species is the peculiar differentiation of the nuclear membrane. The nucleus is surrounded by a typical double membrane of which the inner one has a dense fibrillar layer apposed to it. In mature trophozoites, tubular expansions without inner layer arise from the double membrane; the same type of nuclear membrane occurs in another species, Thalicola salpae.     

Chronology of the ultrastructural modifications during the growth of Gregarina blaberae]

In an ultrastructural study the development of the sporozoite as well as the growth and development of the trophozoite of Gregarina blaberae were followed in the course of experimental infections of larvae of the cokroach Blaberus craniifer. The spectacular growth involved the transformation within 18 days of the sporozoite, measuring 15 X 1 micronm, to a cephaline--trophozoite affixed to the intestinal epithelium--of 250 micronm length and 65 micronm diameter. The sporozoite's ultrastructure is not different from that of sporozoites of other Sporozoa studies to date--the conoid and dense bodies are present. The pellicle consists of 3 membranes, but there are some interruptions in the internal membrane complex. The first dictyosomes are formed from the nuclear envelope. The migration of the nucleus and of the dense bodies, followed by the regression of all the structures characteristic of the sporozoites, and the establishment of a cortical zone that comes to cover the epimerite, take place within 48 h after infection and mark the transformation of the sporozoite into the trophozoite. Development of the cephaline involves the formation of the epicytic folds, which occurs at the base of the deutomerite, starting on the 3rd day of development. A regular system of longitudinal or epicytic folds is formed over the entire surface of the gregarine. On the 4th and 5th days of development, a vacuolar system and a chondriome become differentiated in the epimerite, while a fibrillar septum separates the protomerite from the deutomerite. The next stage, starting on the 6th day, is characterized by distribution of polysaccharide reserves between these 2 segments. The model studied allows us to determine the role of the epimerite in the parasite's nutrition, as well as the development of the chondriome and of the cortical membranes in the course of the vegetative growth phase of the cephaline gregarine.