Morphology of urogenital system in female Echinopardalis atrata (Acanthocephala)

Four major areas of the urogenital system of Echinopardalis atrata are examined: (1) capsular protonephridial system, (2) uterine bell complex, (3) uterus, (4) vagina. Photomicrographs of cross sections from wax preparations depict morphological changes along the length of this system. Diagrammatic illustrations show relationships between excretory ducts and oviducts in the uterine bell complex. Relative positions of dorsal and ventral ligament accessory cells, median wall cells, and sheathing syncytium are also shown in this complex. The common oviduct and excretory canal join to form a ciliated urogenital canal that empties into the lumen of the uterus along the latter's anterior mid-dorsal surface. The excretory bladder is located on the inside mid-dorsal surface of the bell wall and is serviced by 2 nephridial canals--1 from each of 2 capsular protonephridia. The vagina affixes the posterior terminus of the uterus to the tegument and consists of an internal and external sphincter surrounding a hypodermal lining.     

Ultrastructure of the protonephridial system, of Anoplodiscus cirrusspiralis (Monogenea Monopisthocotylea).

The flame bulb is formed by a terminal cell and a proximal canal cell. The weir consists of interdigitating ribs all of which form one circle, i.e. alternating ribs do not have distinctly 'internal' or 'external' positions. Cytoplasmic cords are absent and all ribs, i.e. those continuous with the proximal canal cell and those continuous with the terminal cell, form external leptotriches. At least some external leptotriches have interconnected branches extending along the flame bulb. Internal leptotriches are not branched and arise from the basal perikaryon of the terminal cell. In the cytoplasmic cylinder at the tip of the flame bulb, structures resembling incomplete septate junctions were seen. However, neither the cytoplasmic cylinder nor the small protonephridial capillaries contain complete septate junctions as found in all other Monogenea Polyopisthocotylea, Monogenea Monopisthocotylea, Trematoda Aspidogastrea and Trematoda Digenea examined to date. In the lack of a septate junction, Anoplodiscus resembles Udonella, Amphilinidea, Gyrocotylidea and Eucestoda. However, the presence in this species of rudimentary septate junctions in the small capillaries and of complete junctions in larger ones indicates that complete junctions have been secondarily lost. Anoplodiscus resembles the Monogenea and Trematoda in the presence of lamellae in the larger protonephridial ducts. For the first time in a monogenean, the ultrastructure of the excretory bladder is described. A nucleated convoluted duct opens through a narrow connecting duct into the bladder, which in turn opens through a narrow connecting duct into the excretory pore lined by tegument. Convoluted duct, connecting ducts and bladder are lined by a lamellated epitheliu.(ABSTRACT TRUNCATED AT 250 WORDS)     

On the Early Development of the Protonephridial Systems in Some Species Belonging to the Genera Diphyllobothrium, Triaenophorus and Schistocephalus (Cestoda, Pseudophyllidea)

Malmberg, G. {Department of Zoology, University of Stockholm, Stockholm, Sweden.) On the early development of the protonephridial systems in some species belonging to the genera Diphyllobothrium, Triaenophorus and Schistocephalus {Cestoda, Pseudophyllidea). Zool. Scripta 1 (5): 227–228, 1972.–The protonephridial systems of coracidia (oncospheres) and procercoids of four Diphyllobothrium species, of Triaenophorus nodulosus (Pallas) and of Schistocephalus solidus (Muller) were studied. In the oncospheres of Diphyllobothrium and Schistocephalus the two flame bulbs of the primary protonephridial system were present, but not in the oncospheres of Triaenophorus. In Schistocephalus the two flame bulbs were found to be inactive in the oncosphere (studied inside the coracidium), but very active in the youngest procercoids, which may imply that the primary protonephridial system does not start its function until the oncosphere has entered the copepod body cavity. The primary protonephridial system of the Triaenophorus procercoids was totally (most specimens) or partly reduced. The secondary protonephridial system, however, began developing more or less simultaneously with the integumental hooklets, the cercomer and the first calcareous bodies, which is in accordance with what is described concerning Diphyllobothrium. The ciliated, excretory bladder described by Rosen in 1919 was found to be a posteriorly open invagination, surrounding the “cercomer shaft”. Reverse bends of the posterior main canals of the secondary system are located closely around the wall of, though very likely not emptying into this invagination.     

Ultrastructure of the Flame Bulbs and Protonephridial Capillaries of Artioposthia sp. (Platyhelminthes,Tricladida, Geoplanidae)

The protonephridial terminal complex of Artioposthia is formed by one or two terminal cells, each with a nucleus located in the lateral wall of the flame bulb, and probably two proximal canal cells forming the wall of the protonephridial capillary. The weir is restricted to the proximal parts of the flame bulbs and consists of convoluted slits separated by thick cytoplasmic columns. Cross-striated ciliary rootlets running parallel with and obliquely or transversely to the longitudinal axis of the flame bulbs strengthen the walls of the flame bulbs and, to a lesser degree, that of the capillary. Numerous cristate mitochondria are present in the terminal and proximal canal cells. Cytoplasmic processes extend from the terminal cells into the adjacent tissue, and narrow internal leptotriches extend from the cytoplasm of the terminal cells into the lumen of the flame bulbs. The wall of the capillary contains many interconnected, liquid filled spaces that communicate with the lumen of the capillary, and two septate junctions. Phylogenetic implications of the findings are discussed.     

Ultrastructure of the flame bulbs and protonephridial capillaries of Prorhynchus (Lecithoepitheliata, Prorhynchidae, Turbellaria)

The flame bulb of Prorhynchus is formed by a single cell. Its nucleus is not located in the cytoplasm at the base of the flame. Cilia of the flame have cross-striated hollow ciliary rootlets converging towards their tips. The maximum number of cilia counted was 13. The weir consists of a single row of longitudinal ribs that contain longitudinal filaments and possess regularly arranged protrusions along their surface appearing as transverse bands in horizontal section. A 'membrane' of extracellular material extends between the ribs. and loose material fills the places between the ribs, with a denser layer midway between adjacent ribs. Distally, the ribs fuse to form a continuous tube without a junction. Small protonephridial capillaries lack junctions, larger ducts have lateral flames and patches of long microvilli. Large excretory ducts open into a ciliated and lamellated cavity which is connected by a narrow canal to the excretory pore. The terminal part of the canal close to the pore possesses many cilia and microvilli. Phylogenetic implications of the findings are discussed.     

Ultrastructure of the protonephridial system of regenerating Stenostomum sp. (Plathelminthes,Catenulida)

Summary The ultrastructure of the flame bulbs, protonephridial capillaries and duct of fully developed and regenerating Stenostomum sp. is described. Flame bulbs are formed by a single cell whose nucleus is located basally or laterally to the weir. The weir is formed by a single row of transverse ribs connected by a thin membrane, apparently of extracellular matrix. Internal leptotriches arise from the proximal cytoplasm and extend in a (usually) single row along the weir and into the lumen of the distal cytoplasmic tube. Many or all leptotriches do not fuse with the distal cytoplasm. Two cilia are each anchored in the proximal cytoplasm by a cross-striated vertical and lateral rootlet, the latter bent forward and extending for some distance into one of the two cytoplasmic cords along the weir. Each cord contains the lateral rootlet in its proximal part, as well as many microtubules. The distal cytoplasmic tube contains two (longitudinal) junctions, i.e. lines of contact between cell processes of the same, terminal cell. Occasionally, more than two junctions were seen, apparently due to branches of the terminal cell in contact with each other. Flame bulbs join capillaries lined by several canal cells type I, containing few or no microvilli but lateral flames. Such capillaries join a duct (or ducts?) lined by canal cells type II with many long microvilli. The large protonephridial duct is lined by numerous cells with lateral flames and many long microvilli. In regenerating tissue (10.5 hours after cutting) some flame bulbs were free, i.e. not connected to capillaries, and some capillaries openly communicated with the surrounding intercellular space. In the presence of a single row of ribs in the weir, of internal leptotriches, and of vertical and lateral ciliary rootlets, the flame bulb of Stenostomum sp. resembles that of other Plathelminthes much more closely than hitherto thought. The species differs from non-catenulid plathelminths mainly in the large number of glandular cells lining the large protonephridial ducts, in the transverse orientation of the ribs in the weir and in the presence of only two cilia in the flame.     

An ultrastructural study of the cercarial excretory system in Bucephaloides gracilescens and Prosorhynchus squamatus

The ultrastructure of the flame cells, capillaries, collecting tubes, excretory bladder, excretory atrium, caudal vesicle, lateral caudal ducts and excretory pores of cercariae of Bucephaloides gracilescens (Rudolphi, 1819) Hopkins, 1954 and Prosorhynchus squamatus Odhner, 1905 (Digenea: Bucephalidae) is described. Both species are essentially similar except for some details. The terminal parts of the protonephridia have all the structural features that are typical of trematodes. The collecting tubes in the cercarial body are composed of cells that are wrapped around the lumen. The main collecting tubes are joined to the excretory bladder syncytium by septate junctions. Features of P. squamatus excretory bladder epithelium indicate that it is involved in secretory activity, but this is not the case in B. gracilescens. In both species the luminal surface of the excretory bladder epithelium is increased by lamellae, and the basal plasma membrane forms invaginations. In the bladder syncytium of P. squamatus both apical lamellae and basal invaginations are more developed and mitochondria are also more numerous. The excretory atrium is lined by a syncytium with nucleated cytons located in the surrounding parenchyma. The atrium lining is not continuous with the body tegument and possesses specific secretory inclusions and a thick glycocalyx. Septate junctions connect the atrium syncytium to the excretory bladder epithelium at its anterior end and to the syncytial excretory epithelium lining the caudal vesicle and the lateral caudal ducts at its posterior. In the excretory pores the caudal duct syncytium is joined to the tegument by septate desmosomes.     

Ultrastructure of the protonephridial system of Polystomoides malayi Rohde and P. renschi Rohde (Monogenea: Polystomatidae)

Rohde K. 1973. Ultrastructure of the protonephridial system of Polystomoides malayi Rohde and P. renschi Rohde (Monogenea : Polystomatidae). International Journal for Parasitology3: 329–333. Polystomoides malayi and P. renschi have three types of protonephridial flames. The first type is a typical flame cell with internal and external ribs connected by a weir membrane without nephrostomes, and with internal and external leptotriches. The second type is a flame cell complex consisting of at least two flames reaching into a common cavity. The third type is a non-terminal (= lateral) flame in the protonephridial ducts, consisting of loosely arranged cilia many of which have lateral tube-like extensions and whose tips have irregularly arranged filaments gradually decreasing in number. The number of cilia in all types of flames varies. The smallest capillaries are strongly convoluted and have a smooth or slightly reticulated surface, the larger ducts have strongly reticulated walls and single cilia may be found in the cavities of the reticulum.     

Hymenolepis diminuta: a comparison between young developing, and small, destrobilated worms in the rat intestine

Newly in vitro excysted tapeworms of Hymenolepis diminuta (Cestoda, Cyclophyllidea), 1- to 3-day-old worms and destrobilated worms from rat intestines were investigated by means of light microscopy (LM) and scanning electron microscopy (SEM). It was found that the scolex of 1- and 2-day-old worms had shallow suckers with smooth brims, while 3-day-old and older worms, including destrobilated worms, had deep suckers with puckered brims. The posterior end of 1- and 2-day-old worms had a central cone-shaped structure not present in 3-day-old and older, or destrobilated worms. The repairing of the posterior end and the protonephridial system after excystation or destrobilation was much the same. Tissue remnants moved into the centre of the posterior end, resulting in an indentation with a pore to the exterior. The indentation and its pore became connected to the emptying canals of the protonephridial system, i.e. they developed into the excretory bladder and pore respectively.     

扩张莫尼茨绦虫(绦虫纲:圆叶目)的原肾管及原肾管概念的评述

本研究应用透射电子显微镜研究了扩张莫尼茨绦虫原肾管的细胞学特征 ,莫尼茨绦虫原肾管的焰茎球为一个过滤器结构 ,类似于“挡河坝”样构造 ,此构造由端细胞和近管细胞外突形成的肋条 (或称杆 )相互交错排列而成。肋条之间由细胞外物质构成的“膜”结构连接 ,过滤作用通过该“膜”发生。焰细胞与近管细胞交界处有裂缝或孔与细胞外的结缔组织 (实质组织 )相通 ;原肾管的毛细排泄管细胞质索之间没有隔状联结 ;毛细排泄管及排泄管的管腔内有大量珠状微绒毛突起以增加表面积。从扩张莫尼茨绦虫及其它一些无脊椎动物原肾管的研究结果表明 ,原原肾管概念将焰细胞作为封闭的盲端已不再合适 ,需要进行修订 ,建议修订为 :原肾管是一种焰细胞系统 ,通常由焰细胞、管细胞和肾孔细胞组成 ,焰茎球作为过滤装置与周围的结缔组织 (实质组织 )有或没有裂缝 (孔 )相通     

PROTONEPHRIDIA

(1) The flame cell of platyhelminths is a composite organ formed from two cells. One cell contains a large nucleus and bears the flagella which form the flame. The other cell which contributes the barrel is the first tubule cell. There is a region of interdigitation between the two cells at the top of the barrel and the interdigitations are joined along their length by desmosomes. The tubule lumina are extracellular, the smaller tubules, at least, being formed by encircling projections from a single cell, joined at their tips by desmosomes. Cestodes apparently have no desmosomes in their tubule walls so that the tubule lumina may be intracellular. The tubules of most platyhelminths are lined by folds or microvilli, and flagella may be present in the lumen. The protonephridia of nemertines, entoprocts and priapulids appear to be of this type. (2) Direct evidence of the physiological role of flame cell systems is limited. There is, for example, no proven instance of the production of urine hypo-osmotic to body fluids by any fresh-water platyhelminth or nemertine. Endoparasitic platyhelminths are apparently unable to osmoregulate. The relative permeability of the body surface of marine, fresh-water, terrestrial and parasitic platyhelminths and nemertines may be related to protonephridial function. It seems highly likely that the function of the flame cell is to filter interstitial fluid, separating water and crystalloids from macromolecules. The ultrafiltrate produced then flows down the tubules as a result of the hydrostatic pressure generated by the beating of flame flagella, or as a result of peristaltic waves of the whole body generated by the musculature of the worm. The fluid may be modified in the canal lumen by both active and passive resorption of solutes or the secretion of material from the walls into the lumen. Experiments with the larger platyhelminths suggest that the main function of the system is to remove organic metabolites from the interstitial spaces of the deeper tissues of the worm by a mechanism more efficient than simple diffusion. (3) The flame bulbs of rotifers are fan-shaped and the nucleus is in the tubule not the cap. The barrel of the flame bulb is composed of a series of columns in scalloped formation, each arc of the scallop being supported by a cytoplasmic pillar. A membrane interconnects the columns and each column is linked to its neighbouring central pillar by fibrils. The tubules leading from the flame bulbs are a complex system of three to four multinucleate cells. They empty into a contractile bladder. The protonephridia of acanthocephalans and gastrotrichs may be of this type. (4) The mode of action of flame bulbs is probably to filter the pseudocoelomic fluid which is then modified by selective reabsorption in the tubule system. Rotifers are able to osmoregulate and this may be the chief function of their protonephridia. (5) Solenocytes are morphologically diverse, usually with a cytoplasmic cap containing a nucleus, and a long tubule, in the lumen of which lie one or two flagella. The walls of the tubule are pierced by fenestrations, probably the site of fluid ‘filtration’. (6) Kümmel (1962) has suggested that the many types of terminal organ are the result of divergent evolution from a single ancestral type. We suggest that protone-phridial terminal organs can be divided on structural grounds into three or four different groups which are probably not inter-related. This would mean that the apparent structural similarities which do appear would be the result of convergent evohtion imposing a conformity based on functional requirements.     

The anatomy of the circumgenital scent gland of Saguinus fuscicollis (Callitrichidae, Primates)

In the adult male Saguinus fuscicollis , the scrotal skin and the area above the root of the penis are raised in a sharply defined cushion, which extends cranially into a rectangular suprapubic pad. The circumgenital area of the adult female resembles that of the male, except that the suprapubic pad is relatively and absolutely larger. A complex glandular organ, composed of holocrine and apocrine glands, is located beneath the epidermis of the circumgenital skin. In males, specialized holocrine glands associated with hair follicles predominate. They form a layer, 2-3 mm deep beneath the epidermis. These holocrine glands have a complex alveolar structure and possess numerously branched excretory ducts. Each group of glands empties into a common duct which enters the hair follicle. In males, the apocrine glands are located predominantly at the periphery of the glandular pad and between the scrotal and perineal areas. The excretory ducts of most apocrine glands empty on to the skin surface in close spatial association with hair follicles. However, independent openings were also observed. In females, the specialized holocrine glands resemble those of males but are more frequently interspersed with apocrine glands. The apocrine glands are larger and much more numerous than in males, especially in the region of the labia majora. Gonadectomy of an adult male and female resulted in a reduction in the size of the holocrine glands but had much less effect on the apocrine glands of the scent organ. In addition, the sexual dimorphism in gland histology was retained years after castration.     

Description and life-cycle of Thrinascotrema brisbanica n. g., n. sp. (Digenea: Plagiorchiida), a parasite of the freshwater turtle Elseya latisternum from Australia,and the erection of the family Thrinascotrematidae

A new genus and species, Thrinascotrema brisbanica, is proposed to accommodate a plagiorchiidan trematode parasitic in the stomach of the freshwater turtle Elseya latisternum. The distinctive taxonomic features of the parasite are the shape and extent of the excretory bladder, and the stenostomate arrangement of the excretory collecting ducts in the adult, cercaria and metacercaria together with a cercarial protonephridial formula of 2(12+12+12)+(12+12+12). The life-cycle is three- host and aquatic. The pulmonate snail Glyptophysa gibbosa served as both a first and second intermediate host and tadpoles of Limnodynastes peronii, Adelotus brevis and Bufo marinus, and the snail Austropeplea lessoni also served as second intermediate hosts. Eggs were fully embryonated and infective when laid, but did not hatch until eaten by the snail. Cercariae first emerged 55 days after infection at 24-28 °C. They were sluggish swimmers and survived for about 48 hr. They attached firmly to the skin of snails and tadpoles on contact and began to penetrate the skin after a short exploratory migration. Metacercariae survived in snails and tadpoles for at least 3 months. It is concluded that Thrinascotrema is best placed within a new family, the Thrinascotrematidae (Digenea: Plagiorchiida), based on the unusual morphology of the excretory system.     

The kidney,adrenocortical homolog,and corpuscles of Stannius in the cockscomb pricklebackAnoplarchus purpurescens

The morphology of the kidney, adrenocortical homolog, and the corpuscles of Stannius was examined in the cockscomb prickleback,Anoplarchus purpurescens, a marine teleost which inhabits the intertidal zone. The paired kidneys of this fish are fused throughout most of their length, there is essentially a single posterior cardinal vein on the right side, they possess renal corpuscles, and there is no distal segment of the tubule. The tubule is specialized, in descending order, into ciliated neck and two proximal segments before entering the system of collecting tubules and ducts. The cells of the latter system are specialized for mucous secretion, as are cells of the main excretory ducts, the paired archinephric ducts. Tubulogenesis occurs in the kidneys in close apposition to the archinephric ducts. The presumptive adrenocortical homolog is located around the posterior cardinal veins in the head kidney while paired corpuscles of Stannius are confined to the posterior end of the kidney. All of the above features are consistent with those found in the kidneys of many other marine teleosts.     

Two atavistic characters of some Lumbriculidae and their importance for the classification of Oligochaeta

The rudimentary atria, and the posterior sperm funnels and sperm ducts, which occur in some species of the Lumbriculidae, are discussed. It is shown that the posterior location of funnels and sperm ducts is the result of a forward shift of the atria, which refutes Stephenson's supposition that the Lumbriculidae is the most archaic family of the present-day Oligochaeta.     

Ultrastructural immunocytochemical localization of two hydatid fluid antigens (antigen 5 and antigen B) in the brood capsules and protoscoleces of ovine and equine Echinococcus granulosus and E. multilocularis.

The unlabelled antibody method was used in the ultrastructural localization of two hydatid fluid antigens, antigen 5 and antigen B, in brood capsules and protoscoleces of Echinococcus granulosus and E. multilocularis. Antigen 5 was found in the parenchyma cells of the protoscolex and brood capsule wall and to a lesser extent in the walls of the flame cells and collecting ducts of the excretory system and in the surrounding interstitial material. It is suggested that, while some excretion of this antigen may occur from the protoscolex, it could also be liberated into the cystic cavity by degeneration of protoscoleces and parenchymal cells of the brood capsule wall. Antigen B was found mainly in the distal cytoplasm and perinuclear cytoplasm of the tegument anterior to the suckers. It is apparently secreted to the outside and was present in the brood capsule contents; it adheres to the anterior surface and the posterior periodic acid-Schiff (PAS)-positive glycocalyx of the protoscolex and to the inner surface of the brood capsule wall. The protoscolex tegument posterior to the suckers was negative. The parenchyma cells of the protoscolex and brood capsule wall were also positive although the intensity of the reaction product was variable.     

Development of the excretory system in the polyplacophoran mollusc,Lepidochitona corrugata: The protonephridium

A single pair of protonephridia is the typical larval excretory organ of molluscs. Their presence in postlarval developmental stages was discovered only recently. We found that the protonephridia of the polyplacophoran mollusc, Lepidochitona corrugata, achieve their most elaborate differentiation and become largest during the postlarval period. This study describes the protonephridia of L. corrugata using light and electron microscopy and interactive three‐dimensional visualization. We focus on the postlarval developmental period, in which the protonephridia consist of three parts: the terminal part with the ultrafiltration sites at the distal end, the voluminous protonephridial kidney, and the efferent nephroduct leading to the nephropore. The ultrafiltration sites show filtration slits between regularly arranged thin pedicles. The ciliary flame originates from both the terminal cell and the duct cells of the terminal portion. The efferent duct also shows ciliation. The most conspicuous structures, the protonephridial kidneys, are voluminous swellings composed of reabsorptive cells (“nephrocytes”). These cells exhibit strong vacuolization and an infolding system increasing the basal surface. The protonephridial kidneys, previously not reported at such a level of organization in molluscs, strikingly resemble (metanephridial) kidneys of adult molluscan excretory systems. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

Ultrastructure and histochemistry of the protonephridial system of juvenile Paramphistomum epiclitum and Fischoederius elongatus (Paramphistomidae: Digenea) during migration in Indian ruminants.

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and 1992. Ultrastructure and histochemistry of the protonephridial system of juvenile Paramphistomum epiclitum and Fischoederius elongatus (Paramphistomidae: Digenea) during migration in Indian ruminants. International Journal for Parasitology 22: 1103–1115. The protonephridial system of juvenile Paramphistomum epiclitum and Fischoederius elongatus consists of a bilaterally symmetrical arrangement of primary, secondary and tertiary ducts which connect individual flame cells with a simple common bladder. Primary and secondary ducts are formed from columns of adjoining cells which provide an epithelial lining, whose luminal surface is elaborated with either short tubercles or lamellae. Groups of cilia project from the luminal surface at frequent intervals along secondary ducts. By contrast, the tertiary ducts and bladder are lined with a nucleated syncytium which ends at a junctional complex formed with the terminal canal. The latter is continuous with the tegumental syncytium and opens at a nephridiopore on the postero-dorsal surface. Tertiary ducts of mature cercariae contain concretions which are voided by migrating juveniles in whose tertiary ducts lipids are progressively accumulated. Evidence for the role of protonephridia in excretion and possibly in osmoregulation and ionic balance is currently examined.     

Ultrastructure of excretory system in <Emphasis Type="Italic">Bothrioplana semperi</Emphasis> (Platyhelminthes,Turbellaria)

The ultrastructure of flame bulbs and epithelium of excretory canals in Bothrioplana semperi (Turbellaria, Seriata) have been studied. The flame bulbs consist of two cells, the terminal cell and the proximal canal cell. The weir is formed by two rows of longitudinal ribs. The ribs of the internal row originate from the flame cell, external ribs are formed by the proximal canal cell. Each external rib has a remarkable bundle of microfilaments, originating in the cytoplasm of the first canal cell distally to the bases of external ribs. Membrane of internal ribs is marked by small electrondense granules, separate or fused to an electron-dense layer, continuous to dense “membrane,” connecting both external and internal ribs. Sparse internal leptotrichs originate from the bottom of the flame bulb cavity. External leptotrichs are lacking. Septate junction is present only in proximal canal cell at the level of tips of cilia. The apical surface of the canal cell bears rare short microvilli. The basal membrane of canal cells forms long invaginations that may reach nearly the apical membrane. The epithelium of excretory canals lacks the cilia. The ultrastructure of flame bulbs and epithelium of the excretory canals in B. semperi shares representatives of suborder Proseriata (Seriata). The contradiction exists in interpretation of the structure of flame bulbs in Proseriata. Ehlers and Sopott-Ehlers assumed that the external ribs are derivatives of the proximal canal cell and internal ones are outgrowths of the terminal cell, while Rohde has found conversely: the external ribs are outgrowths of the terminal cell, the internal ones are outgrowths of the proximal canal cell. However, the illustrations provided by Rohde do not enable to ascertain what cells the internal and external ribs derive from, while illustrations provided by Ehlers justify his interpretation. The order of weir formation in B. semperi confirms the viewpoint of Ehlers. The implication of ultrastructure of flame bulbs in Proseriata, especially of the order of flame bulb formation, in the Platyhelminthes phylogeny has been discussed.     

Ultrastructural characteristics of the protonephridial terminal organ and associated ducts of adult specimens of the Aspidogastrea, Digenea and Monogenea, with comments on the relationships between these groups

Transmission electron microscopical observations were made on the protonephridial terminal organ and associated ducts of three adult trematodes, the aspidogastrean Aspidogaster limacoides Diesing, 1835 and the digeneans Azygia lucii (Müller, 1776) and Phyllodistomum angulatum Linstow, 1907, and the monogenean Ancyrocephalus paradoxus Creplin, 1839. Previously unreported ultrastructural details of the terminal organ of adult trematodes include multiple contact sites (septate junctions and zonulae adherentes) between the membranes of the terminal and adjacent canal cells. Septate junctions traverse the epithelial cytoplasm of the canal wall, and the same type of septate junctions are observed within the cytoplasmic cord at the level of the tip of the flame tuft in both longitudinal and oblique sections of all three trematode species studied. In the monopisthocotylean Ancyrocephalus paradoxus, the absence of any junctions in the cytoplasmic cord and the presence of septate junction within all of the protonephridial ducts are reported. On the basis of the small number of monogenean species in which these features have been studied, in relation to the size of the group, there seems to be a high diversity in some characters of the protonephridial terminal organ. The study confirms that the Aspidogastrea and Digenea possess the same morphology of their protonephridial terminal organ and, although this differs slightly from that of most members of the Monogenea so far studied, it supports previous views on the close relationship of these groups.