THE MECHANISM OF THE NEPHRIDIAL APPARATUS OF PARAMECIUM MUL TIMICRONUCLEATUM : I. Expulsion of Water from the Vesicle

Recent analysis of the mechanism of the nephridial apparatus of Paramecium multimicronucleatum by high-speed cinematography (300 fps at x 250) confirms the observations by electron microscopy (Schneider, 1960) that once the pore is opened, the vesicle is invaginated by adjacent cytoplasm and is emptied by collapsing under pressure from that cytoplasm, aided perhaps by pressure of the fibrils which anchor the ampullae to the excretory canal. There is no indication of active contraction of the vesicle or its membrane. There is no permanent pore to the vesicle. The vesicle is closed by a sealing of the ruptured membrane where it is in contact with the pellicular excretory canal. At onset of expulsion of vesicular fluid the membrane across the basal opening of the excretory canal is ripped along one semicircular portion of the excretory pore and is driven up against the opposite wall as a flap while the water rushes out. A constriction of the vesicular and cell membranes at the base of the excretory canal reseals the opening.     

THE MECHANISM OF THE WATER EXPULSION VESICLE OF THE CILIATE TETRAHYMENA PYRIFORMIS

Analysis of high-speed (150 frames/sec) cinematographs of the filling and expulsion of the water expulsion vesicle of Tetrahymena pyriformis shows that the vesicle fills as water is pumped into it by contractions of at least four ampullary sacs which are continuous with the endoplasmic reticulum. When filled, the vesicle is pressed against its two excretory pores by cyclotic movements of the cytoplasm. This pressure closes the apertures of the ampullae, preventing backflow from the vesicle into them, and also spreads the pellicle of and at the pore, thereby stretching and rupturing the pore-sealing membrane. The vesicle is then invaginated by the cytoplasmic pressure, driving fluid out of the pore. The pore-sealing membrane then reforms, apparently by constriction, and the vesicle is again filled. Electron micrographs show that crisscrossed pore-microtubules extend from the pore to the openings of the ampullae, anchoring the vesicle in place. Each pore is surrounded by a stack of at least 11 ring-microtubules, to which the anchoring pore-microtubules are attached. The pore-microtubules appear to exert tension which assists in spreading the pore, aiding cyclotic pressures in rupturing the pore-sealing membrane. A possible mechanism for the cyclotic pressure and ampullary contraction is proposed.     

Functional anatomy of the valves in the ambulacral system of sea urchins (Echinodermata,Echinoida)

Summary The water vascular system of sea urchins is examined with special reference to the valves positioned between the radial vessel and the ampullae of the tube feet. The lips of the valve protrude into the ampulla. Thus the valve functions mainly like a check valve that allows the unidirectional flow of fluid towards the ampulla. Each ampulla-tube foot compartment acts as a semi-autonomous hydraulic system. The lumina of the ampulla and the tube foot are lined with myoepithelia except for the interconnecting channels that pierce the ambulacral plate. The contraction of the ampulla results in an increasing hydraulic pressure that protrudes the tube foot, provided that the valve is closed. The retraction of the tube foot results in a backflow of fluid independent of the condition of the valve. The lips of the valve are folds of the hydrocoel epithelium. The pore slit lies in the midline. The perradial faces of the lips are covered with the squamous epithelium of the lateral water vessel. The ampullar faces are specialized parts of the ampulla myoepithelium. Turgescent cells which form incompressible cushions take the place of the support cells. The valve myocytes run parallel to the pore slit and form processes that run along the base of the ampulla and the perradial channel up to the podial retractor muscle. The findings lead to the hypothesis of multiple control of the ampulla-tube foot system: (1) The mutual activity of the ampulla and the tube foot is indirectly controlled by the lateral and podial nerves which release transmitter substances that diffuse through the connective tissue up to the muscle layers. (2) A muscle-to-muscle conduction causes the simultaneous contraction of the ampulla or the podial retractor muscles. (3) The valve muscles are directly controlled by the processes of the valve myocytes which make contact with the podial retractor. In extreme conditions a backflow of hydrocoel fluid towards the radial water vessel occurs.     

Acidovorax-like symbionts in the nephridia of earthworms

Dense accumulations of bacteria in the excretory organs, nephridia, were first described more than 75 years ago in members of the annelid family Lumbricidae (earthworms). These nephridial symbionts were assumed to play a role in the degradation of proteins in the excretory fluid for nitrogen recycling. In the present study, the phylogenetic affiliation of the nephridial bacteria of the earthworms Lumbricus terrestris, Aporrectodea tuberculata, Octolasion lacteum and Eisenia foetida was resolved. The 16S rRNA gene sequences of the symbionts formed a monophyletic cluster within the genus Acidovorax. Similarity between symbiont sequences from different host species was 95.5-97.6%, whereas similarity was> 99% between symbiont sequences from individuals of the same species. Densely packed bacteria were detected in the ampulla of the nephridia by fluorescence in situ hybridization (FISH) using Acidovorax-specific oligonucleotide probes. No other bacterial cells could be found by FISH, although a few sequences other than Acidovorax had been found by PCR and cloning. These results suggest that the Acidovorax-earthworm symbiosis is a stable, host-specific association that has evolved from a common bacterial ancestor. Given the close phylogenetic relationship of the symbionts to proteolytic, free-living Acidovorax species, they may indeed play a role in protein degradation during nitrogen excretion by earthworms.     

The microscopic anatomy and ultrastructure of the nephridium of the sipunculan Themiste hexadactyla Satô 1930) (Sipuncula: Sipunculidea)

The microscopic anatomy and ultrastructure of the nephridia of the sipunculan Themiste hexadactyla (Satô, 1930) from the Sea of Japan were studied by the histological and electron microscopic methods. The fine structures of the ciliary funnel, muscular “tongue,” excretory sac, and excretory tube of the nephridium were described. The ultrastructural features of the excretory epithelium, cupola-shaped epithelial infoldings, excretory canals, and muscular layer in the extracellular matrix of the nephridial wall were examined and described in detail. The ultrastructure of the nephridial coelomic epithelium composed of podocytes with long processes and multiciliary cells was also examined and illustrated. Characteristic cell contacts between the processes of podocytes, viz., paired “double diaphragms,” were described and illustrated for the first time.     

Nippostrongylus brasiliensis and Haemonchus contortus: Function of the excretory ampulla of the third-stage larva

An improved technique for measuring the water content of nematodes is described using an electronic interferometer. Changes in phase of a laser beam passing through a known pathlength of the nematode have been used to measure the refractive index and hence the water content and relative volume of the animal. Third-stage larvae of Nippostrongylus brasiliensis and Haemonchus contortus which possess an excretory ampulla, differed from second-stage larvae lacking this ampulla in requiring a greater fall in the osmolarity of artificial tap water before there was a significant increase in their water content. Increases in the pulsation frequency of the ampulla also occurred in less hypotonic solutions than those required to increase the water content of the third-stage larvae. The ampulla pulsation frequency of third-stage larvae of N. brasiliensis increased after locomotor activity in hypotonic tap water and locomotory wave frequency of third-stage larvae of N. brasiliensis was independent of the extent of hypotonicity for a range of solutions that reduced wave propogation by its second-stage larva. The results suggest that the ampulla is an adaptation to hypotonic conditions favouring a volume homeostasis that is required for optimal locomotor activity of the third-stage infective larvae of these nematodes.     

THE FINE STRUCTURE OF ACANTHAMOEBA CASTELLANII : I. The Trophozoite

The fine structure of the trophozoite of Acanthamoeba castellanii (Neff strain) has been studied. Locomotor pseudopods, spikelike "acanthopodia," and microprojections from the cell surface are all formed by hyaline cytoplasm, which excludes formed elements of the cell and contains a fine fibrillar material. Golgi complex, smooth and rough forms of endoplasmic reticulum, digestive vacuoles, mitochondria, and the water-expulsion vesicle (contractile vacuole) are described. A canicular system opening into the water-expulsion vesicle contains tubules about 600 A in diameter that are lined with a filamentous material. The tubules are continuous with unlined vesicles or ampullae of larger diameter. Centrioles were not observed, but cytoplasmic microtubules radiate from a dense material similar to centriolar satellites and are frequently centered in the Golgi complex. Cytoplasmic reserve materials include both lipid and glycogen, each of which amounts to about 10% of the dry weight.     

Rhythmic contractions of the ampullar epidermis during metamorphosis of the ascidian Molgula occidentalis

Summary The ampullae of Molgula occidentalis are hollow, tubular extensions of the epidermis. They are ensheathed by a secreted tunic. When they grow out shortly after settlement, the ampullae spread the tunic over the substratum to form a firm attachment for the sessile juvenile. A simple squamous epithelium forms the thin ampullar walls. A glandular, simple columnar epithelium forms the distal tip of each ampulla. The glandular cells probably secrete the adhesive that attaches the tunic to the substratum.Repetitive, peristaltic contractions pass from the base to the distal end of each ampulla. Microsurgery, time-lapse cinemicrography and TEM have been used to analyze this phenomenon. The contractions are mediated by a layer of 4–8 nm microfilaments in the base of the ampullar epithelium.Each juvenile has 7–9 ampullae which contract at different frequencies. Isolated ampullae continue to contract normally for several days. Thus each ampulla has an intrinsic rhythm. Microsurgical experiments suggest that there is no specific region within an ampulla with unique pacemaker properties. It is proposed that communication via gap junctions allows the coordination of ampullar cells into a well organized peristaltic wave.     

FINE STRUCTURE IN RELATION TO FUNCTION IN THE EXCRETORY SYSTEM OF TWO SPECIES OF VIVIPARUS

The fine structure of the excretory system of 2 species of Viviparushas been studied by scanning and transmission electron microscopy.The structure of the heart is described and its mode of operationdiscussed. The structure and function of the kidney and ureterare discussed and it is concluded that the nephridial glandhas hypertrophied (Received 30 October 1978;     

Morphology and function of Malpighian tubules and associated structures in the cockroach, Periplaneta americana.

This paper describes the different regions of the Malpighian tubules and the associated structures (ampulla, midgut, ileum) in the cockroach, Periplaneta americana. There are about 150 tubules in each insect. Each tubule consists of at least three parts. The short distal region is thinner than the other parts and is highly contractile. The middle region comprises most of the tubule length and is composed of primary and stellate cells. Primary cells contain numerous refractile mineral concretions, while stellate cells have smaller nuclei, fewer organelles, simpler brush border, and numerous multivesicular bodies. Symbiont protozoa are sometimes present within the lumen of the middle region near where it opens into the proximal region of the tubule. The latter is a short region that drains the tubular fluid into one of the six ampullae. These are contractile diverticula of the intestine located at the midgut-hindgut junction. The ampulla is highly contractile, and consists of a layer of epithelial cells surrounding a cavity that opens into the gut via a narrow slit lined by cells of unusual morphology. The proximal region of the tubule and the ampulla resemble the midgut in that they have similar micromal origin and reabsorptive function for the proximal region of the tubule and for the ampulla. A number of inclusions found within the tubule cells are described, including peroxisomes and modified mitochondria. Current theories of fluid transport are evaluated with regard to physiological and morphological characteristics of Malpighian tubules. The possible role of long narrow channels such as those between microvilli and within basal folds is considered, as is the mechanism by which these structures are formed and maintained. Also discussed is the role of peroxisomes and symbionts in the excretory process.     

Progesterone secretion by the post-ovulatory rat cumulus oophorus

This study was designed to determine whether cumulus oophorus cells secrete progesterone. Immature PMS-primed, hCG-treated rats were used. Their cumuli were isolated from pre-ovulatory (no hCG) and peri-ovulatory (after hCG) follicles, and from post-ovulatory oviducal ampullae. Treatment with hCG increased progesterone secretion by almost two-and-one-half-fold. It was speculated that the cumulus oophorus secretion of progesterone modifies the accumulation of fluid in the ampulla, thus providing the medium in which fertilization takes place.     

Excretion in the house cricket (Acheta domesticus): ultrastructure of the ampulla and ureter

An ultrastructural analysis of the ampulla and ureter of the cricket, Acheta domesticus, is presented. The excretory system of the cricket is unusual in that the 112 Malpighian tubules do not attach directly to the gut, but fuse to form a bladder-like ampulla which is joined to the colon by a muscular ureter. The ampulla consists of two cell types, primary and regenerative. Primary cells secrete large numbers of membrane-bound vesicles into the lumen and also appear to be involved in fluid reabsorption. Regenerative cells are very small and form a layer just beneath the basal lamina of the ampulla. They are believed to differentiate and replace sloughed off primary cells. The ureter is a muscular tube lined with cuticle which connects the ampulla (endoderm) with the colon (ectoderm). The probable origin and significance of the morphological modifications of the excretory system are discussed.     

The structure of the excretory system of the infective larva of Haemonchus contortus

The excretory system of the infective larva of Haemonchus contortus consists of a tubular H-system with two excretory cells. The excretory cells contain electron-dense granules which may be a source of exsheathing fluid. Video microscopy indicates that the pulsation of the excretory ampulla is due to a cycle of filling and emptying controlled by the excretory valve. The apparent functional similarity between this system and the contractile vacuole complex of protozoa is discussed.     

Comparison of the lateral line and ampullary systems of two species of shovelnose ray

The anatomical characteristics of the mechanoreceptive lateral line system and electrosensory ampullae of Lorenzini of Rhinobatos typus and Aptychotrema rostrata are compared. The spatial distribution of somatic pores of both sensory systems is quite similar, as lateral line canals are bordered by electrosensory pore fields. Lateral line canals form a sub-epidermal, bilaterally symmetrical net on the dorsal and ventral surfaces; canals contain a nearly continuous row of sensory neuromasts along their length and are either non-pored or pored. Pored canals are connected to the surface through a single terminal pore or additionally possess numerous tubules along their length. On the dorsal surface of R. typus, all canals of the lateral line occur in the same locations as those of A. rostrata. Tubules branching off the lateral line canals of R. typus are ramified, which contrasts with the straight tubules of A. rostrata. The ventral prenasal lateral line canals of R. typus are pored and possess branched tubules in contrast to the non-pored straight canals in A. rostrata. Pores of the ampullae of Lorenzini are restricted to the cephalic region of the disk, extending only slightly onto the pectoral fins in both species. Ampullary canals penetrate subdermally and are detached from the dermis. Ampullae occur clustered together, and can be surrounded by capsules of connective tissue. We divided the somatic pores of the ampullae of Lorenzini of R. typus into 12 pore fields (10 in A. rostrata), corresponding to innervation and cluster formation. The total number of ampullary pores found on the ventral skin surface of R. typus is approximately six times higher (four times higher in A. rostrata) than dorsally. Pores are concentrated around the mouth, in the abdominal area between the gills and along the rostral cartilage. The ampullae of both species of shovelnose ray are multi-alveolate macroampullae, sensu Andres and von Düring (1988). Both the pore patterns and the distribution of the ampullary clusters in R. typus differ from A. rostrata, although a basic pore distribution pattern is conserved.     

Fellodistomidae and Zoogonidae (Digenea) of deep-sea fishes of the NW Atlantic Ocean

The following species are described from fishes in deep-waters of the northwestern Atlantic Ocean: Fellodistomidae: Steringophorus furciger from Antimora rostrata, Coryphaenoides (Lionurus) carapinus, Lycenchelys paxillus, L. verrillii and Lycodes atlanticus; S. blackeri from Xenodermichthys copei, S. haedrichi n. sp. from Porogadus milesi, characterised by its lobate testes, sucker-ratio and long vitelline fields Megenteron crassum from Dicrolene intronigra; Zoogonidae: Brachyenteron rissoanum n. sp. from Polyacanthonotus rissoanus, characterised by the ovary position, the saccular seminal vesicle, the marginal genital pore and egg-size; Koiea notacanthi n. g., n. sp. from Notacanthus (?) chemnitzi, characterised by the Y-shaped excretory vesicle and the posteriorly placed testes.     

鲶鱼（Parasilurus asotus）小窝器官胚胎后发育的定量研究

鲶鱼的小窝器官(电感觉器官)、其壶和感觉毛细胞的数量在胚胎后有很大增长,新的器官在一定时期内大量发生,单个器官内的壶和感觉毛细胞的数量则持续增加,器官形态有较大变化。本文统计了不同体长的鲶鱼三者的数量变化。实验表明,器官、壶和毛细胞可分别从2.5厘米体长时的1400、1400和8400增加到55厘米体长时的2.5万、20万和120万。这种数量的增长,特别是感觉毛细胞在胚胎后的增长机制和发生条件是值得注意的。本文研究了小窝器官的神经支配模式。     

EXOCYTOSIS OF LATEX BEADS DURING THE ENCYSTMENT OF ACANTHAMOEBA

Cells of Acanthamoeba castellanii (Neff) are known to form mature cysts characterized by a cellulose-containing cell wall when transferred to a nonnutrient medium. Amebas which engulfed latex beads before encystment formed mature cysts essentially devoid of bead material. The encystment of bead-containing cells appeared to be similar to that of control cells since no important differences between the two were observed with respect to cellular levels of glycogen or protein, cellulose synthetase activity, the amount of cyst wall polysaccharide formed, or the percentage of cysts formed. Actinomycin D and cycloheximide inhibited encystment as well as bead expulsion. Ultrastructural analysis revealed that the beads, which initially were contained in phagocytic vesicles, were released from the cell by fusion of vesicular membranes with the plasma membrane. Exocytosis was observed in cells after 3 hr of encystment, with most of the beads being lost before cyst wall formation. Each bead-containing vesicle involved in expulsion was conspicuously demarcated by an area of concentrated cytoplasm, which was more homogeneously granular than the surrounding cytoplasm. Beads were not observed in the cytoplasm of mature cysts but were occasionally found in the cyst wall.     

Structure and Role of the Renette Cell and Caudal Glands in the Nematode Sphaerolaimus gracilis (Monhysterida)

Ultrastructure of the renette cell and caudal glands was studied in the free-living aquatic nematode Sphaerolaimus gracilis. The renette cell occurred posterior to the esophageal-intestinal junction and opened through an ampulla to a ventral pore behind the nerve ring. The caudal gland system of the tail consisted of two gland cells opening through separate pores and 2 to 3 other gland cells of a different type opening through a common pore. The renette cell and the two caudal gland cells were similar and both contained secretory granules, 0.5-1.5 μm in diameter. The material released attached the nematode to the substrate. The renette ampulla was surrounded by a specialized cell, the ampulla cell, which had characteristics of myoepithelium. A plug or valve structure connected to the ampulla cell may regulate the output of the secretory material. The ampulla cell is able to contract and thus is probably under direct neuronal control. Other cells in the renette ampulla region of body cavity were termed supporting cells. Living, cold-relaxed nematodes were attached to sediment particles in the renette pore region and at the tail tip. Release from sediment particles was mechanical at the renette cell discharge site but appeared to be chemical at the caudal gland. In behavioral experiments, nematodes in a water current had the ability to release a thread from the caudal glands while maintaining contact with a sediment particle attached to the tail end. If the thread was strong enough, it also could be used to change location. Nematodes anchored by the thread from the caudal glands to a sediment particle could float in water currents until they attached themselves to another sediment particle with the help of secretions from the renette cells.     

Ampulla Morphogenesis in Anural and Urodele Molgulid Ascidians

Vascular ampulla morphogenesis was studied in two anural-developing molgulids and one urodeledeveloping molgulid. In all three species, each juvenile developed one longer ampulla (termed the primary ampulla) and several shorter ampullae (termed secondary ampullae). Ampulla growth was accompanied by the formation of contraction rings that moved in a proximal to distal direction. Contraction ring formation was initiated by the epidermal cells situated in the proximal region of each ampulla. The formation of an expanding bubble-like region within each lumen preceded ring formation. These rings moved at approximately 120 μm/min. Rings were produced for several days until the ampullae retracted towards the body wall.
In all three species, hemoblast cells were evident at day 4 within the developing mantle sinus (hemocoel). Ampulla growth was studied by positioning chalk particles on the tunic surface near the tips of ampullae. During the growth phase, chalk particles moved towards the body of the zooid. This report is the first to describe contraction ring formation and the polarized transport of tunic components during ampulla morphogenesis in two anural ascidian species.