Life Cycle of Eimeria ferrisi Levine & Ivens, 1965 in the Mouse, Mus musculus

SYNOPSIS. The life cycle of Eimeria ferrisi is described from experimentally infected Mus musculus. The prepatent period was 3 days and the patent period was 3–4 days. The endogenous stages were found only in the cecum and colon. Three generations of schizonts were found. Mature 1st-generation schizonts first seen 24 hr postinoculation (PI) measured 10.9 (7–14) × 10.2 (6–13) μm and had 9.6 (7–14) merozoites. Some 2nd-generation schizonts had uninucleate merozoites and others had multinucleate merozoites. The former were first seen in small numbers 36 hr PI and were most abundant 48 hr PI. They measured 9.6 (5–13) × 7.9 (6–12) μm and had 18 (6–25) merozoites. Schizonts with multinucleate merozoites were seen 72 hr PI. Mature 3rd-generation schizonts were seen 72 hr PI. They measured 14.0 (12–18) × 11-0 (9–13) μm and had 12.5 (5–16) merozoites. Macrogamonts were first seen in 72 hr sections. Each young macrogamont had a large nucleus with a prominent nucleolus. Only one type of cytoplasmic granule appeared to be involved in the formation of the oocyst wall. Mature macrogamonts were 11.0 (5–14) × 10.0 (6–13) μm. Crescent-shaped bodies were observed in the parasitophorous vacuole of trophozoites and young macrogamonts. Early microgamonts were first recognized at 96 hr by the presence of darkly stained and irregularly shaped nuclei. Usually, mature microgametes were arranged in long, narrow whorls at the periphery of the microgamont or in whorls at the surface of 2–5 compartments.     

Scanning Electron Microscopy of Schizogony in Eimeria tenella

SYNOPSIS. Developing 2nd- and 3rd-generation schizonts of Eimeria tenella were found in the ceca of chicks infected orally with sporulated oocysts. Several free 2nd-generation schizonts, which varied in diameter from 11 to 21.6 μm, were found on the epithelial surface of the cecum. Some schizonts appeared to have lost merozoites. Other schizonts were intact, one of which was surrounded by an unbroken membrane that followed the contours of the merozoites. Third-generation schizonts, much smaller than 2nd-generation schizonts and with fewer merozoites, were found only on cut or fractured surfaces of the cecal tissue. Third-generation merozoites appeared shorter and thicker than those of the 2nd-generation and were attached to the schizont residuum. A form with conical protuberances and another with 4 triangular segments were found; they were believed to be developing stages 3rd-generation schizonts.     

In Vitro Cultivation of the Vascular Phase of Sarcocystis singaporensis

To establish an in vitro culture system for the precystic phase of Sarcocystis singaporensis, we initially tested various excysting fluids for sporocysts. An excysting fluid containing 2.5% bovine taurocholate and 10% bile of the specific intermediate host, Rattus norvegicus, in RPMI medium was the most suitable resulting in excystation of 80% of the sporozoites. Subsequently, we identified brain endothelial cells and pneumonocytes of the rat to promote growth of sporozoites to schizonts. Hepatoma, fibroblastic, or myoblastic cells were not suitable for the parasite's development. First-generation schizonts were seen at days 3-10 postinoculation (PI); a distinct second peak of schizogonic development only occurred in endothelial cells at days 14-18 PI. First-generation schizonts were 26.0 (± 3.8) μm in diameter and contained 32-50 merozoites, second-generation schizonts measured 34.4 (± 10.6) μm and contained 54-72 merozoites. Merozoite yield at large-scale culture conditions (75 cm² flasks) using pneumonocytes as host cells was relatively low. Ultrastructurally, sporozoites and merozoites were quite similar to corresponding stages of other Sarcocystis species. With regard to host cell specificity and developmental kinetics, in vitro cultivation showed close similarities to the situation in vivo.     

Development and Ultrastructure of First-Generation Meronts of Sarcocystis cruzi in Calves Fed Sporocysts from Coyote Feces*

SYNOPSIS. The development of Sarcocystis cruzi Hasselmann (syn. S. fusiformis Railliet) meronts was studied in seven 7- to 10-day-old calves killed 4, 7, 11, 15, 22, 25 and 28 days postinoculation (DPI) with 5 × 10⁷ sporocysts from feces of coyotes. No meronts were found 4 and 7 DPI. Young and intermediate meronts with 1–16 nuclei were found in endothelial cells of arteries in mesenteric lymph nodes, but not in kidneys 11 DPI. Mature meronts were noted in endothelial cells of arteries, arterioles, or capillaries of many organs of calves killed 15 to 25 DPI. No first-generation meronts were found 28 DPI. By electron microscopy, all stages of the first-generation merogony were found free within the host cell cytoplasm and not within a parasitophorous vacuole. The appearance of intranuclear spindles preceded the formation of merozoites by endopolygeny. Mature meronts measured 41.0 × 17.5 (34–50 × 15–24) μm, contained ～ 100–350 merozoites, and had 2 to 4 relatively small residual bodies, 2.8 μm in diameter. Merozoites measured 6.3 × 1.5 (5.5–7 × 1 μm) and contained most of the organelles characteristically found in coccidian merozoites. Micropores were observed in merozoites, but not in young and intermediate meronts. Merozoites were seen free in the lumen of blood vessels, in intracellular areas, and free within the host cell cytoplasm.     

Observations on First-Generation Schizogony of Leucocytozoon caulleryi in Chickens

ABSTRACT. First and second generation schizogony of Leucocytozoon caulleryi occurred in chickens infected with sporozoites. First generation schizogony was studied by light and electron microscopy. First-generation schizonts were first detected in capillary endothelial cells in the spleen, lung, liver, and bursa of Fabricius between 3 and 6 d post-sporozoite inoculation (DPI). The schizonts ranged from 15 to 65 μm in diameter and were surrounded by a thin pellicle. Early schizonts contained numerous round or oval nuclei, endoplasmic reticulum, and mitochondria. The schizonts reached maturity 5 DPI and produced first-generation merozoites which were released into the peripheral bloodstream. The merozoites. which were infective to chickens, measured 7.1 μm in length. They were slender and had a large nucleus, a mitochondrion, and an apical complex consisting of three polar rings, rhoptries, numerous micronemes. The morphology of first-generation merozoites was different from that of second-generation merozoites.     

The asexual pre-cyst development of Sarcocystis tenella in experimentally infected specific pathogen-free lambs

Twenty-two lambs raised under sporozoa-free conditions were infected at weaning with 0.25–2.0 million Sarcocystis tenella sporocysts obtained from dogs and then necropsied at intervals between 1.3 h and 41 days post-inoculation (dpi). Fixed and frozen sections from 47 different tissues from each lamb were examined respectively by a variety of histochemical stains and by indirect fluorescent-antibody staining. The remnants of excysted sporocysts were found within the gastro-intestinal tract between 1.3 h and 3 dpi. No enteric proliferative stage of the parasite was detected. First-generation meronts (schizonts) were detected from 6 to 19 dpi within the endothelial cells of arterioles in most organs and tissues. The meronts were undifferentiated from 6 to 9 dpi but were mature in appearance from 12 to 19 dpi (measuring 22.3 × 13.4 μm and containing 18–28 merozoites). Second-generation meronts were detected from 21 to 34 dpi within the endothelial cells of capillaries throughout the entire body. They were undifferentiated from 21 to 23 dpi but appeared mature from 25 to 34 dpi (measuring 15.2 × 10.6 μm and containing 18–38 merozoites). Several smaller meronts were then detected at 36 dpi within cells of the mononuclear phagocytic system. They were all mature in appearance (measuring 7.4 × 5.1 μm and containing 6–9 merozoites) and are thought to have formed facultatively following the incorporation of some second-generation merozoites into phagocytic cells. Only developing cysts were then detected at 41 dpi throughout the cardiac and skeletal musculature. Elements in both first- and second-generation merozoites stained markedly with haematoxylin and eosin, periodic acid-Schiff's, alkaline Giemsa-colophonium and basic fuchsin stains. However, only second-generation meronts and developing cysts exhibited strong specific reactions with the fluorescent-antibody stain.     

Development of Eimeria meleagrimitis Tyzzer from sporozoites and merozoites in turkey kidney cell cultures

Sporozoites and 1st-, 2nd-, and 3rd-generation merozoites of Eimeria meleagrimitis were inoculated into primary cultures of turkey kidney cells. In vitro-excysted sporozoites developed into mature macrogamonts in 8 days; in vivo-excysted sporozoites developed into 2nd- or 3rd-generation schizonts within 5 to 7 days. First-generation merozoites obtained from infected turkeys produced mature 2nd-generation schizonts within 24 h. Second-generation merozoites from turkeys produced mature macrogamonts and oocysts within 72 h, whereas 3rd-generation merozoites produced these stages within 48 h. The oocysts that developed from 3rd-generation merozoites sporulated at 25 C and were infective for turkeys. The timing of the early stages and the intervals between schizogonic generations in cultures were comparable with those in turkeys. Morphologic parameters, however, indicated that some differences existed between in vitro and in vivo development. Second- and 3rd-generation schizonts and gamonts that developed after inoculation of cultures with merozoites were similar to stages in turkeys. Oocysts, however, were significantly smaller (P less than 0.05) in cultures. All stages that developed after inoculation of cultures with sporozoites were smaller (P less than 0.05) than their in vivo counter parts.     

Development of Eimeria meleagrimitis Tyzzer from Sporozoites and Merozoites in Turkey Kidney Cell Cultures*

SYNOPSIS. Sporozoites and 1st-, 2nd-, and 3rd-generation merozoites of Eimeria meleagrimitis were inoculated into primary cultures of turkey kidney cells. In vitro-excysted sporozoites developed into mature macrogamonts in 8 days; in vivo-excysted sporozoites developed into 2nd- or 3rd-generation schizonts within 5 to 7 days. First-generation merozoites obtained from infected turkeys produced mature 2nd-generation schizonts within 24 h. Second-generation merozoites from turkeys produced mature macrogamonts and oocysts within 72 h, whereas 3rd-generation merozoites produced these stages within 48 h. The oocysts that developed from 3rd-generation merozoites sporulated at 25 C and were infective for turkeys. The timing of the early stages and the intervals between schizogonic generations in cultures were comparable with those in turkeys. Morphologic parameters, however, indicated that some differences existed between in vitro and in vivo development. Second- and 3rd-generation schizonts and gamonts that developed after inoculation of cultures with merozoites were similar to stages in turkeys. Oocysts, however, were significantly smaller (P < 0.05) in cultures. All stages that developed after inoculation of cultures with sporozoites were smaller (P < 0.05) than their in vivo counter parts.     

The Life Cycle of Isospora felis Wenyon, 1923, a Coccidium of the Cat*

SYNOPSIS. A pure strain of Isospora felis derived from a single oocyst was used to study the endogenous cycle. One and a half to two-month-old laboratory-reared, coccidia-free kittens were used thruout the study. The endogenous stages occurred in the epithelial cells of the distal parts of the villi in the ileum and occasionally duodenum and jejunum. All stages lay above the host cell nucleus. There were 3 asexual generations. The 1st generation schizonts were 11–30 by 10–23 μ when mature and contained 16–17 banana-shaped merozoites 11–15 by 3–5 μ. They became mature in 96 or sometimes in 120 hours. The 1st generation merozoites entered new host cells, rounded up and formed 2nd generation schizonts. These formed within themselves 2–10 or more spindle-shaped bodies resembling 1st generation merozoites in shape and size. These were 2nd generation merozoites. They were uninucleate 120 hours after inoculation, but by 144 hours they became larger, multinucleate and some lost their elongate shape and became ovoid. They were then 3rd generation schizonts. They were 12–16 by 4–5 μ. Each formed up to 6 or more banana-shaped merozoites 6–8 by 1–2 μ. The 3rd generation schizonts and merozoites developed within the same host cell and parasitophorous vacuole as the 2nd generation schizonts and merozoites. Mature schizonts containing only 3rd generation merozoites appeared 144 hours after inoculation, were most abundant 168 hours after inoculation, and might be present as late as 216 hours after inoculation. They were 14–36 by 13–22 μ and contained 36 to more than 70 merozoites. The 3rd generation merozoites entered the sexual cycle. The mature microgametocytes were 24–72 by 18–32 μ and contained a central residuum and a large number of microgametes 5–7 by 0.8 μ with 2 posteriorly-directed flagella. The mature macrogametes were 16–22 by 8–13 μ. Gametogony occurred 144–216 hours after inoculation. The prepatent period was 168–192 hours and the patent period 10–11 days. Peak oocyst production occurred on the 6th day of the patent period.     

An Ultrastructural Study of First- and Second-Generation Merogony in the Coccidian Sarcocystis tenella1

ABSTRACT. Sporocysts of the coccidian Sarcocystis tenella were originally isolated in the feces of a coyote. Sporocysts used for inoculation of lambs were obtained from experimentally infected dogs. At 14, 16, and 19 days postinoculation (DPI) of lambs with the sporocysts, various developmental stages of first-generation meronts were found within cells located between the endothelium and internal elastic membrane of mesenteric arteries. At 19, 21, and 25 DPI, second-generation merogony occurred in cells associated with capillaries and arterioles of kidney glomeruli and convoluted tubules. Meronts of both generations were bounded by a double pellicular membrane and were situated free in the host cell cytoplasm. Merozoites formed by endopolygeny that involved multiple intranuclear spindles of a single, large irregular nucleus. First-generation meronts measured 22.6 × 17.1 μm (19–28.7 × 7.5–24 μm) and contained 120–240 merozoites, which measured 7.1 × 1.6 μm (4.8–7.5 × 1.3–1.8 μm). Corresponding values for second-generation meronts were 13.2 × 9.2 μm (8.3–15 × 7–13.5 μ), 32–80, and 5.8 × 1.7 μm (5.6–6.2 × 1.4–2.2 μm).     

Pre-Erythrocytic Development and Associated Host Responses to Haemoproteus meleagridis (Haemosporina: Haemoproteidae) in Experimentally Infected Domestic Turkeys12

ABSTRACT. Two generations of pre-erythrocytic schizogony occurred in skeletal and cardiac muscle of domestic turkeys infected with sporozoites of Haemoproteus meleagridis. First generation schizonts reached maturity approximately five days post-inoculation (DPI) and developed in capillary endothelial cells and myofibroblasts. The schizonts ranged from 12 to 20 μm in diameter and produced long (5–6 μm), slender merozoites. Early second generation schizonts were first detected in capillary endothelial cells between 5 and 8 DPI. They were cylindrical and ranged in size from 5 to 8 μm in diameter and up to 28 μm in length. Second generation schizonts which reached maturity by 17 DPI were surrounded by a thick, hyaline wall and were packed with numerous spherical merozoites less than 1 μm in diameter. Mature megaloschizonts were fusiform, ranged from 30 to 113 μm in diameter, and extended as much as 465 μm along the long axis of muscle fibers. Merozoites developed as buds from cytomeres that formed between 8 and 14 DPI. Infected turkeys developed a moderate to severe myositis within 5 DPI and were lame in one or both legs. The myositis was associated with the necrosis of scattered groups of muscle fibers. Muscle fibers surrounding mature megaloschizonts were swollen and hyaline. Megaloschizonts were surrounded occasionally by fibroblasts and infiltrates of mononuclear cells. The morphology and site of development of mature megaloschizonts of Haemoproteus meleagridis are contrasted with those of other avian haemosporidians.     

Observations on the Endogenous Stages of Eimeria confusa Joseph, 1969 from the Grey Squirrel Sciurus carolinensis*

SYNOPSIS. Stages in the endogenous cycle of Eimeria confusa from the grey squirrel, Sciurus carolinensis, are described from mixed infections with another species, Eimeria lancasterensis. All corresponding stages were markedly different in the 2 species. In E. confusa infections, the parasites were located below the host cell nuclei of the epithelial cells of the villi of the jejunum and ileum. Mature schizonts were ellipsoidal, averaged 20.9 × 18.6 μm and had 18–30 merozoites. The mature microgamonts measured 34.3 × 24.7 μm and had hundreds of microgametes. Mature macrogametes were ovoid, averaged 31.3 × 25.6 μm, and contained 2 kinds of plastic granules.     

Toxoplasma gondii-like schizonts in the tracheal epithelium of a cat

Toxoplasma gondii-like schizonts were found in tracheal epithelium of an 8-yr-old male cat. The parasites were located in parasitophorous vacuoles within the host cell cytoplasm, divided by schizogony, contained periodic acid-Schiff-positive granules, and reacted with anti-T. gondii serum but not with anti-Neospora caninum serum. Mature schizonts were 7.0 x 5.9 microns (5-10 x 4-10 microns; n = 22) and contained 4-16 merozoites. The merozoites were approximately 5 x 1 microns.     

The life cycle of Eimeria falciformis var. pragensis (Sporozoa: Coccidia) in the mouse, Mus musculus

The life cycle of Eimeria falciformis var. pragensis, established from a single oocyst, is described in experimentally infected mice (Mus musculus). The coccidium had a prepatent period of 7 days and a patent period of 10--16 days. Oocysts were spherical to ellipsoidal in shape and measured 21.2 x 18.3 micron. Sporulation time was 3 to 3.5 days. Sporocysts measured 12.2 x 7.2 micron and contained a circular to avoid granular sporocyst residuum measuring 5.5 X 5.0 micron. One, 2 or 3 circular to rectangular polar granules were observed within each sporulated oocyst. The endogenous stages developed primarily in the cecum and colon and only occasionally in the lower ileum. Four generations of schizonts were found. Mature 1st-generation schizonts, first observed 48 hr postinfection (PI), measured 17.8 x 12.3 micron and had 12 merozoites that measured 13.3 x 2.0 micron. Mature 2nd-generation schizonts appeared 78 hr PI. They measured 10.2 x 9.3 micron and had 8 merozoites measuring 5.0 x 1.6 micron. Mature 3rd-generation schizonts appeared first at 114 hr PI and measured 17.5 x 10.2 micron and had 10 merozoites that measured 12.4 x 1.8 micron. Mature 4th-generation schizonts appeared first at 144 hr PI. They measured 18.2 x 15.3 micron and had 18 merozoites. The merozoites of the 4th-generation schizont were 4.5 x 1.2 micron. Mature macrogamonts and microgamonts developed simultaneously appearing at 156 hr PI. Macrogamonts measured 16 x 14.5 micron and microgamonts were 18.2 x 15.3 micron. In experimentally infected rats (Rattus norvegicus), development of E. falciformis var. pragensis progressed only as far as mature 1st-generation schizonts.     

The Life Cycle of Eimeria vermiformis Ernst,Chobotar and Hammond, 1971 in the Mouse Mus musculus1

SYNOPSIS. The life cycle of Eimeria vermiformis from the mouse Mus musculus is described from experimental infections. The prepatent period was 7 days, and the patent period 7–22+ days. Endogenous stages were in the lower 2/3 of the small intestine. Two generations of schizonts were found. Mature 1st generation schizonts, seen 4 days after inoculation, were 16–25 × 9–16 μ and had long vermiform merozoites. Mature 2nd generation schizonts were first seen 5 days after inoculation. They were 8–18 × 7–14 μ (mean 11.2 × 13.1 μ). Mature microgametocytes, 17–32 × 12–25 μ, were present 6 days after inoculation. Macrogametes with plastic granules were found at the same time. The life cycle of E. vermiformis is compared with those of other species of Eimeria from Mus.     

Life Cycle of Isospora rivolta (Grassi, 1879) in Cats and Mice*

SYNOPSIS. The endogenous development of Isospora rivolta (Grassi) was studied in cats fed oocysts, and was compared with the endogenous cycle after feeding them mice infected with I. rivolta. For the mouse-induced cycle, 14 newborn cats were killed 12 to 240 h after having been fed mesenteric lymph nodes and spleens of mice. Asexual and sexual development occurred throughout the small intestine, in epithelial cells of the villi and glands of Lieberkuhn. The number of asexual generations was not determined with certainty, but there were at least 3 structurally different meronts. Type I meronts appeared at 12–48 h postinoculation (HPI). They were 8.5(6–13) × 5.1(3–6) μm, contained 2–8 merozoites, and divide by binary division or endodyogeny. Type II meronts were multinucleate merozoite-shaped meronts within a single parasitophorous vacuole. They were found at 48–172 HPI and measured 12.6(9–18) × 9.8(9–13) μm. Individual multinucleate merozoite-shaped meronts were 7–13 × 3–5 μm in sections and contained 2–30 slender (5.5 × 1.0 μm) merozoites. Type III meronts occurred at 72–192 HPI and gamonts at 72–96 HPI. Mature microgamonts measured 11.3(9–15) × 8.0(6–9) μm in sections and up to 21.5 × 14 μm in smears, and contained up to 70 microgametes. Macrogamonts measured 13.3(11–18) × 9.0(5–13) μm in sections and 18 × 16 μm in smears. Oocysts were 10–15 × 9–15 μm in sections and 19.8(17–24) × 18.0(17–23) μm in fixed and stained smears. Unsporulated oocysts in feces were 22.3(18–25) × 19.7(16–23) μm and spomlated oocysts 25.4(23–29) × 23.4(20–26) μm. Sporulation was completed within 24 h at 22–26 C. For the study of the oocyst-induced cycle in cats, 18 newborn cats were killed between 6 and 192 HPI. The endogenous development was essentially similar to the mouse-induced cycle, but merogony and gametogony occurred 12–48 h later than in the latter cycle. Isospora rivolta was pathogenic for newborn but not for weaned cats. Newborn cats fed 10⁵ sporocysts or infected mice usually developed diarrhea 3–4 days after inoculation. Microscopically, desquamation of the tips of the villi and cryptitis were seen in the ilium and cecum in association with meronts and gamonts. For the study of the development of I. rivolta in mice, mice were killed from day 1 to 23 months after having been fed 10⁵–10⁵ sporocysts, and their tissues were examined for the parasites microscopically, and by feeding to cats. The following conclusions were drawn. (A) Isospora rivolta most frequently invaded the mesenteric lymph nodes of mice and remained there for 23 months at least. It also invaded the spleen, liver, and skeletal muscles of mice. This species could not be passed from mouse to mouse. Sporozoites increased in size from ?6.8 × 4.9 μm on day 1 to ?13.4 × 6.9 μm on day 31 postinoculation. Division was not seen. Prepatent period was 4–7 days and patent periods ranged from 2 to several weeks.     

In vitro Development of First-Generation Schizonts of Eimeria canadensis (Bruce, 1921)*†

SYNOPSIS. In vitro development of Eimeria canadensis from cattle was studied in monolayer cultures of various bovine cell lines grown on coverslips in Leighton tubes. Excysted sporozoites were used for inoculation of the cell cultures. Sporozoites entered the host cells within a few minutes, but apart from a reduction in the number of refractile bodies, changed little in appearance during the first 9 days. Beginning at 91/2 days postinoculation, sporozoites developed into sporozoite-shaped schizonts or, less frequently, transformed into trophozoites. Sporozoite-shaped schizonts with as many as 8 nuclei were observed transforming into spheroid schizonts. At 111/2 days, intermediate schizonts had a characteristic single mass of refractile granules and 60–80 nuclei. Deep invaginations, which resulted in the formation of several blastophores, usually occurred when schizonts had about 100 nuclei. Merozoites were formed as a result of radial outgrowth from the surface of spheroid schizonts as well as of blastophores. Mature merozoites were seen 1st after 13 days.     

Endogenous Cycle of the Swine Coccidium Eimeria debliecki Douwes, 1921*

SYNOPSIS. A pure strain of Eimeria debliecki (University of Illinois strain A) established from a single oocyst was used to determine the endogenous cycle. Young parasite-free pigs 2 weeks to 3 months old were used throughout the study. The endogenous cycle was found to take place in the small intestine where the parasites were located in the distal portion of the striated simple columnar epithelial cells of the villi. The first generation schizonts were found in only the jejunum (15% of small intestine). The second generation schizonts and gametes occurred in the jejunum and ileum (70% of small intestine), a slight posterior progression occurring with each stage. The entire cycle required 6.5 days. The schizogonous cycle comprised 2 generations. The first generation schizonts required 2.5 days to reach maturity, measured 8-12 μ, contained 16 merozoites measuring 12-15 μ and had a polar residual mass. The second generation schizonts required 2 days to reach maturity, measured 13-16 μ, contained 32 rotund merozoites measuring 6–8 μ, and had only a few granules of residual material. Gametogony took place in 1.5 days. The macrogametes measured 12-16 μ, and the microgametocytes measured 9-14 μ with microgametes measuring 5–6 μ.     

Endogenous Stages of the Life Cycle of Isospora rivolta in the Dog

SYNOPSIS. Coccidia-free beagle puppies were experimentally infected with a cloned culture of Isospora rivolta oocysts. The endogenous stages were found in the posterior 1/2 of the small intestine, and rarely in the cecum and colon. Maximum numbers of all stages occurred just anterior to the ileocecal valve. Endogenous stages were found in the distal third of the villi, predominantly parasitizing subepithelial cells of the lamina propria; however, stages were occasionally present in epithelial cells. The number of asexual generations could not be determined from their structure, but evidence based on oocyst production suggested that there were at least 2 asexual generations. The schizonts were 17–24 by 12–25 μ and contained 4–24 merozoites, the most common number being 4 or 8. Schizonts with mature merozoites were found as early as 72 hr, but were present in maximum numbers at 96 hr. Merozoites had slender curved bodies and were 10.5–13.4 by 2.3–3.0 μ. Mature gamonts were found by 144 hr. Mature microgametocytes were 13.4 by 8.7 μ and contained 50–70 microgametes. Microgametes had slightly curved tapering bodies (5.8–6.4 by 0.6 μ) with 2 posteriorly directed flagella 11–14 μ long. Mature macrogametes had reticular cytoplasm and a uniformly large nucleus and nucleolus.
The prepatent period was 142–146 hr. The patent period was 13–23 days with an average of 19 days.     

广东艾美虫发育的研究

广东艾美虫寄生于乌鳢的消化道,其发育周期可分为裂体生殖、配子生殖和孢子生殖三个阶段。这三个阶段均在一个寄主体内完成。裂体生殖和配子生殖发生在幽门盲囊和前肠上皮细胞核之上方。成熟裂殖体为球形或椭圆形,含有8—14个香蕉形裂殖子。大配子的整个发育过程没有发现嗜伊红颗粒,嗜碱性颗粒在卵囊壁形成前后发生变化。成熟小配子母细胞内有许多新月形的小配子。孢子生殖在幽门盲囊和整条肠管内进行。