Membranous Sac Research Articles

Fungal sporocarps from Triassic peat deposits in Antarctica

Several different fossil fungi are described from silicified peat deposits collected in Antarctica. Some are characterized by the presence of an interwoven hyphal wall layer surrounding a central cavity devoid of contents. Others show an outer wall layer which is composed of isodiametric cells and a thin acellular inner layer which surrounds membranous sacs or globose spores. The structures of these fossils are interpreted and potential relationships discussed.

Subcellular Fractionation of Prohormone Processing Products in the Bag Cell Neurons

Multiple biologically active peptides arising from a common prohormone are sorted into distinct classes of dense core vesicles within the bag cell neurons of Aplysia californica. In this study, pulse-chase analysis, combined with subcellular fractionation on Percoll gradients, are used to define the location of the prohormone processing events within the secretory pathway. Initial cleavage of the prohormone occurs in a light cellular compartment associated with the Golgi apparatus. The amino-terminal processing intermediate then accumulates in a denser compartment containing small dense cores enclosed in membranous sacs, as well as larger immature vesicles. After 4 h, amino-terminal products are found primarily in a much denser compartment which consists of large and small dense core vesicles. These large and small vesicles can be separated from each other using Percoll gradient centrifugation and are found to be enriched in amino- and carboxy-terminal products, respectively. Lastly, membrane association experiments suggest differential binding to membranes, or integral membrane proteins, as a possible mechanism for sorting of amino- and carboxy-terminal products.

The use of two-dimensional Doppler sonography (color Doppler) in the diagnosis of hydranencephaly

Hydranencephaly, first described by Cruveilhier, may be defined as a rare condition in which the cerebral hemispheres are replaced by membranous sacs filled with cerebrospinal fluid. Cerebral angiography is especially useful in differentiating hydranencephaly and severe hydrocephalus, massive subdural hygromas and alobar holoprosencephaly, but it is no better than other neuroradiological diagnosis methods in the neonate. This report outlines the diagnostic use of two-dimensional Doppler (color Doppler) in a child with hydranencephaly. Color Doppler was performed using an SSA-270A (Toshiba) with a 3.75 MHz phase-array sector scanning probe and no sedation. In this study, color Doppler demonstrated the internal carotid artery in the proximal portion, but the secondary and tertiary branches were not observed. In summary, color Doppler permitted early, easy diagnosis of hydranencephaly. In addition, the use of color Doppler was beneficial in diagnosing other anomalies of the central nervous system in neonates.

Immunoelectron microscopic localization of plateins (alveolar plate proteins) during the morphogenesis of new cell cortex in the ciliate Euplotes

The ciliated protozoan Euplotes possesses a complex membrane-cytoskeletal surface layer, or pellicle, that appears to be a primary determinant of cell form. Flattened membranous sacs, termed alveoli, are arranged in a confluent monolayer just beneath the plasma membrane. Each alveolus contains a discrete polygonal alveolar plate (AP); it is likely that the tightly packed mosaic sheet of APs (together with subalveolar microtubules) provides the rigidity of the cell cortex and dictates the characteristic contours of the cell. This pellicular structure must be duplicated daily during vegetative growth of the cell, following a stereotypical program of cortical morphogenesis the stages of which have been well described at the light microscopic level. At the ultrastructural level, models of new pellicle formation have been presented; both suggest that new alveoli form beneath the expanding plasma membrane by the fusion of numerous specialized membranous vesicles, 0.1-0.4 (μm in diameter, termed “alveolar precursor vesicles” (APVs). It is proposed that the plates form within the growing alveoli by the condensation or polymerization of the electron-dense core material seen within the APVs.

Na+-dependent GABA transport system scavenges endogenous external GABA and prevents desensitization of GABAA receptors in rat cerebrocortical synaptoneurosomes

Muscimol-induced 36Cl- uptake in rat cerebrocortical synaptoneurosomes was reduced upon exposure of the membrane sacs to low Na+ media. This Na+ requirement led us to examine the role of the Na(+)-dependent gamma-aminobutyric acid (GABA) transport system in 36Cl- uptake. Incubation of the synaptoneurosomes with nipecotic acid, a specific inhibitor of the GABA transport system, for 10 min increased the level of endogenous external GABA from less than 10 to 150 microM and induced the same signs of desensitization as observed with high muscimol-treated synaptoneurosomes; a marked reduction of muscimol-induced 36Cl- uptake and an appearance of a slow bicuculline-sensitive 36Cl- uptake, probably due to a continuous recovery of a population of GABAA receptors from desensitization. Similar results were obtained upon dissipation of Na+ electrochemical gradient across the membranes by inhibition of Na+, K(+)-ATPase with ouabain or by blocking energy metabolism with azide or N-ethylmaleimide. We propose that the Na(+)-dependent GABA transport system, its operation being dependent on inwardly directed Na+ electrochemical gradient, is responsible for scavenging endogenous GABA released from the synaptoneurosomes, and thus prevents desensitization of GABAA receptors.

A method for removal of toxic chromium using dialysis-sac cultures of a chromate-reducing strain of Enterobacter cloacae.

A method for removal of toxic hexavalent chromium (chromate: CrO2-4) was developed by use of dialysis-sac cultures of a chromate-reducing strain of Enterobacter cloacae (HO1). E. cloacae strain HO1 cells were put in dialysis (semipermeable membrane) sacs, and the sacs were submerged in water containing toxic CrO2-4. The dialysis sacs allowed CrO2-4 to diffuse into the culture, and CrO2-4 was reduced anaerobically in the dialysis sacs by the E. cloacae cells. Because reduced chromium readily formed insoluble chromium hydroxides in the dialysis sacs, the greater part of reduced chromium was unable to diffuse out through the semipermeable membrane. Thus the dialysis culture of E. cloacae strain HO1 could successfully remove toxic chromium from the surrounding water. If the initial concentration of CrO2-4 was less than 4 mM (208 ppm as chromium), about 90% of the total chromium could be removed from water by the described method.

PATHOLOGICAL FlNDINGS IN CALVES WITH HYDRANENCEPHALY'

This study was based 011 hydranencephalic 22 calves. These calves were obtained Ji'om the provinces of Antalya and İçel during an epizootic period in ı985. The serum neutralizing antibodies against Akabane virus were detected in eighteen blood sera tak en from hydranencepha/ic calves and their mothers by Pirbright Animal Virus Resem'dı Institute (A VRI) in England. Pozitive results for bluetongue virus were also determined in eight of eighteen sera using ELISA. In addition, the bluetongue virus was isolated Ji'om the' blood of two hydranencepha/ic calves by Etlik Animal Disease Research Institute (ADRI) in Turkey. These isolates were identifieel as bluetongue virus serotype 4 by Pirbright AVRI. None the calves showed any remarkable clinical symptoms except b/indness. Macroscopical/y, hemispheres were fil/ed with various amounts of cerebrospinal fluid (CSF). The brain stems were normal in appearance. Changes due to compression were noticed in the thalamus. corpus striatum, hippocampus, tectum mesencephaly and cerebel/um. The displacement and hypoplasia of the pineal body were encountered in two different calves. Obstructioll of the third ventricle due to precipitation of calcium salts was observed in one ca/f. The other macroscopical findings were cystic septum pellucidum, defect of the septum pellucidum and partial absence of the corpus cal/osum. Microscopically, narrow residual hemispheric tissues were scierotic in appearance, although the relatively large tissues had normal histologic strııctures and some areas of residual tissues were composed of only leptomeninges. Generally, residual hemispheric tissues had narrow substantia a/ba protruding to the membranous sacs due to gliosis. Sclerotic appearances were also observed in the promontorium gliosum calami scriptorU of the medulla oblongata in almost all of the cases. The other microscopical findings were subependymal rosettes, gliosis, subcOl.tical cavitations and mild perivascular cujfings. Myelination was normal. These changes were found in all cases except one, that case had nonpurulent encephalitis.

Projections of ventromedial hypothalamic neurons to the midbrain central gray: An ultrastructural study

Ventromedial hypothalamic projections to the midbrain central gray may be involved in the mediation of female reproductive behavior. In order to demonstrate and examine projections of the ventromedial nucleus in the midbrain central gray, in the rat, electrolytic lesions were placed in the ventromedial nucleus and the midbrain central gray was examined for ultrastructural signs of degeneration at various intervals, i.e. 27.5 h and two, four, six and eight days following the lesions. The fine structure of the midbrain central gray of unlesioned animals was also examined to characterize its normal morphology and to establish a baseline with which to compare the effects of the lesion. In unlesioned animals, the neuropil of midbrain central gray contained several synaptic types, with axodendritic synapses appearing to be the most predominant. Dendrites contained well-preserved microtubules. Synaptic endings contained many clear, round vesicles and some contained dense-cored vesicles as well. Neuropil synapses were both asymmetric and symmetric. Cell bodies were characterized by light cytoplasm and had asymmetric and symmetric synapses on their surface. Following electrolytic lesions in the ventromedial nucleus, various types of degenerative patterns were seen in the midbrain central gray, including electron-dense, flocculent, watery, and pinocytotic degeneration. Specific characteristics of degeneration included shrunken, dense axons and endings, clumped synaptic vesicles, abnormally large, dark mitochondria, membranous sacs of various sizes, swollen endings with reduced numbers of synaptic vesicles, and endings and processes containing large numbers of coated vesicles. Some of these signs were already evident at 27.5 h following the lesion. In addition, degenerating postsynaptic processes and cell bodies were seen in the midbrain central gray. At 27.5 h survival time, degenerating dendritic processes often appeared swollen, devoid of microtubules, and contained enlarged mitochondria. At longer survival times neuronal degeneration was observed in the midbrain central gray, characterized by electron-dense cell bodies and pycnotic nuclei. Both degenerating pre- and postsynaptic elements appeared to be engulfed by glial processes. Control lesions in non-hypothalamic regions which project to the midbrain central gray, i.e. nucleus gigantocellularis and pontine reticular formation and in a non-projecting region, i.e. parietal cortex, were performed. Lesions in the nucleus gigantocellularis and parietal cortex had virtually no effect on midbrain gray morphology, and lesions in the pontine reticular formation produced only slight degeneration in the midbrain central gray. These results demonstrate the innervation of the midbrain central gray by the ventromedial nucleus and characterize the nature of the ventromedial hypothalamic projections in the midbrain central gray at the fine structural level. These projections may carry estrogen-dependent signals originating in the ventromedial nucleus to the midbrain central gray.

Permeability and Ultrastructure of Bundle Sheath Cells Isolated from C4 Plants: Structure‐Function Studies and the Role of Plasmodesmata

AbstractBundle sheath cells from leaves of C4 plants can be isolated as strands surrounding vascular tissue. In this form these cells are highly permeable to metabolites and, as a consequence, they have a variety of experimental uses. The present paper reports on anatomical and ultrastructural features of isolated bundle sheath cell strands in relation to their integrity and permeability. This analysis shows that the cells retain a high degree of structural integrity during isolation. The plasmodesmata that originally connected the bundle sheath cytosol with mesophyll cells are apparently also retained in their entirety. However, at the external surface (mesophyll side) a membranous sac was commonly observed protruding from the end of plasmodesmata. The functional integrity of cells and the molecular weight exclusion limit for entry of compounds was assessed by following plasmolysis and cytorrhysis induced by polyethylene glycol solutions of varying molecular weights. Other evidence for the retention of cell compartment semipermeability is also provided.

Identification and location of the structural glycoproteins of a tissue culture-adapted turkey enteric coronavirus.

SummaryThe Minnesota strain of turkey enteric coronavirus (TCV) was grown on a human rectal tumor (HRT-18) cell line in the presence of radiolabeled amino acids and glucosamine to analyse virion structural proteins. In addition to the 52,000 unglycosylated nucleocapsid protein, three major glycoprotein species were found to be associated with the viral envelope. A predominant glycosylated protein with a molecular weight of 22–24,000 represented the transmembrane matrix protein. Larger glycoproteins with apparent molecular weights of 180–200,000 (gp 200), 120–125,000 (gp 120) and 95–100,000 (gp 100) were associated to the characteristic large bulbous projections (peplomers) located at the surface of the virion. The gp 100 and gp 120 species apparently arose from a proteolytic cleavage of gp 200, as suggested by digestion studies with trypsin and chymotrypsin. An additional large glycoprotein with mol.wt. of 140,000 (gp 140), that behaved as a disulfide-linked dimer of a 66,000 molecule, was found to be associated to granular projections located near the base of the large peplomers. Digestion studies with trypsin, bromelain and pronase demonstrated that gp 140 was related to the hemagglutinating activity of the virus. An inner membranous sac or tongue-shaped structure could be visualized in the interior of the viral particles following treatment with pronase. In contrast, trypsin or chymotrypsin treatments resulted in evaginations (“budding”) on the virus surface. Progeny viral particles produced in TCV-infected cell cultures in the presence of tunicamycin lacked both types of surface projections, as demonstrated by electron microscopy and electrophoresis. The matrix protein also appeared to be reduced to its unglycosylated form, concomitant with a considerable loss of its antigenicity. Thus, with respect to its morphological and biochemical characteristics, TCV resembles viruses belonging to the group of mammalian hemagglutinating coronaviruses, but differs in that both types of envelope glycoproteins are N-glycosylated as in case of the avian infectious bronchitis virus.

Changes of the membrane potential in striatal synaptoneurosome, synaptosome and membrane sac preparations induced by glutamate, kainate and aspartate as measured with a cyanine dye DiS-C 2-(5)

The effects of glutamate, kainate and aspartate on the membrane potential of striatal synaptoneurosome, synaptosome and membrane sac preparations were studied by using a potential sensitive cyanine dye DiS-C 2-(5). Excitatory amino acids glutamate and aspartate had a depolarizing effect on synaptoneurosomes, 7.9 μM glutamate and 2.8 μM aspartate produced a half-maximal response. Depolarizations induced by glutamate and aspartate were dependent on the concentration of extracellular sodium ions, a maximal response occurred at around 40 mM of external Na +. Kainate induced a dual effect on synaptoneurosomes. In a standard Na +-based medium a hyperpolarization, likely due to inhibition of a presynaptic sodium-dependent glutamate uptake, predominated over a postsynaptic kainate receptor-mediated depolarization that was observed when electrogenic glutamate uptake was inhibited. This interpretation was supported by results obtained with synaptosome and membrane sac preparations. In a standard Na +-based medium kainate had a hyperpolarizing effect on synaptosomes while in the membrane sac preparation kainate induced a depolarization.

IgE receptor-mediated hydrolysis of phosphoinositides by cytoplasts from rat basophilic leukemia cells.

Cytoplasts (plasma membrane sacs containing cytoplasm, endoplasmic reticulum, and few organelles) were prepared from rat basophilic leukemia cells by treatment with cytochalasin B and centrifugation at 33 degrees C through stepwise gradients of Ficoll. To compare the relative ability of cytoplasts and cells to generate second-messengers (inositol phosphates, Ca2+) in response to stimulation of the high affinity receptor for IgE, we normalized our results per recovered receptor by using the tightly bound IgE as a marker. This marker correlated well with other estimates of plasma membrane recovery. Furthermore, data normalized on this basis correlated well with data expressed as percentage of phosphoinositides hydrolyzed. The purest fraction of cytoplasts (containing about 6% of the receptors) was satisfactorily devoid of organelles and, at early times, generated about 50% as much inositol phosphates per receptor as did the intact, untreated cells. This response of the cytoplasts, like that of the cells, was totally dependent upon aggregation of the receptors. The response by the cytoplasts (in the 5-min time frame which we examined), unlike that of the cells, was not enhanced by the presence of extracellular Ca2+. Furthermore, unlike the cells, the cytoplasts failed to raise their intracellular free Ca2+ levels after addition of polyvalent Ag. This result suggests that aggregation of the receptors may be insufficient, by itself, to open the normal Ca2+ channels.

Effects of Temperature and Water Potential on Germination, Radicle Elongation and Emergence of Mungbean

Controlled environment experiments were performed to determine the effects of temperature and water potential on germination, radicle elongation and emergence of mungbean (Vigna radiata (L.) Wilczek cv. IPB-M79-17-79). The effects of a range of constant temperatures (15-45 °C) and water potentials (0 to -2-2 MPa) on germination and radicle elongation rates were studied using an osmoticum technique, in which seeds were held against a semi-permeable membrane sac containing a polyethylene glycol solution. Linear relationships were established between median germination time (Gtso) and water potential at different temperatures, and between reciprocal Gtso (germination rate) and temperature at different water potentials. Germination occurred at potentials as low as — 2-2 MPa at favourable temperatures (30-40 °C), but was fastest at 40 °C when water was not limiting, with an estimated base temperature (Tb) of about 10 °C. Subsequent radicle elongation, however, was restricted to a slightly narrower temperature range and was fastest at 35 °C. The concept of thermal time was used to develop an equation to model the combined effects of water potential and temperature on germination. Predictions made using this model were compared with the actual germination obtained in a related series of experiments in columns of soil. Some differences observed suggested the additional importance of the seed/soil/water contact zone in influencing seed germination in soil. Seedling emergence appeared to reflect further the radicle elongation results by occurring within a narrower range of temperatures and water potentials than germination. Emergence had an estimated Tb of 12-6 °C and was fastest at 35 °C. A soil matric potential of not less than about — 0-5 MPa at sowing was required to obtain 50% or more seedling emergence.

Development of the Embryonic Envelopes ofMesocestoides lineatus(Cestoda: Cyclophyllidea)

Summary Transmission electron microscopy revealed that the eggs of Mesocestoides lineatus consisted of an oncosphere larva surrounded by various coverings. The outermost of these was the embryonic capsule, which appeared as a thin electron-dense membranous sac. The capsule enclosed inner and outer embryonic envelopes, each of which was syncytial and apparently formed from embryonic blastomeres. The envelopes became increasingly vesiculated during embryogenesis, and were attached to each other by desmosomes by the time the larva was fully formed. An electron-dense intracellular embryophore was produced by the inner envelope; it first appeared under the distal plasma membrane as a series of blocks, which grew and fused to form a thick unbroken layer. Early in development, the proximal plasma membrane of the inner envelope was connected to the larval epithelium by a multilaminate membrane complex that was ultrastructurally similar to a continuous junction. At the end of embryogenesis, this appeared to detach...

The hemimastigophora ( Hemimastix amphikineta nov. gen., nov. spec.), a new protistan phylum from gondwanian soils

The morphology, morphogenesis and ultrastructure of Hemimastix amphikineta nov. gen., nov. spec, are described. This species occurred in some Australian and in 1 Chilean soil, but was absent from more than 1000 soil samples from Laurasian localities. Thus, it has probably a restricted Gondwanian distribution. Hemimastix amphikineta is a small (14-20 × 7-10 μn), colourless organism that looks distinctly Ciliophora-like because of its posteriorly located contractile vacuole and its 2 longitudinal somatic kineties each composed of about 12 cilia-like flagella. These 2 kineties are interposed between 2 large plicated and microtubule-bearing pellicular plates which are arranged inversely mirror-image like ("diagonal symmetry"). Hemimastix amphikineta has saccular to tubular mitochondrial cristae and complex extrusomes. It has 2 microtubular systems and a membranous sac associated with each kinetid. The nucleolus persists throughout nuclear division. A permanent cytostome-cytopharyngeal complex, pharyngeal rods, striated fibres, mastigonemes, and a paraflagellar rod are absent. This unique combination of characters dictates a very separate position for H. amphikineta within the known protists. Thus, the phylum Hemimastigophora nov. phylum (Hemimastigea nov. cl. and Hemimastigida nov. ord.), is established to include H. amphikineta and possibly Spironema multiciliatum Klebs, 1892. The structure of the pellicle and the nuclear apparatus of H. amphikineta indicate some relationship with the Euglenophyta. However, clear evidence for a certain affinity is lacking. Thus, the Hemimastigophora are placed in an incertae sedis position within the kingdom Protista Haeckel, 1866.

Molecular species of glycerolipids of Ehrlich ascites cells and of their fat granules.

Ehrlich ascites cells were grown in mice and were isolated by centrifugation of the ascites fluid. The cells were lysed with distilled water, and the floating fat particles were collected by centrifugation. The particles contained about 90% neutral and 10% polar lipid. The neutral lipid was made up of about 50% triacylglycerol, 30% alkyldiacylglycerol, 3% cholesteryl esters, 3% free cholesterol and 4% free diacylglycerols. The phospholipid fraction was comprised of about 50% phosphatidylcholine, 35% phosphatidylethanolamine, 10% sphingomyelin and small amounts (less than 5% total) of serine and/or inositol phosphatides. The triacylglycerol and alkyldiacylglycerol fractions possessed total carbon number and fatty acid compositions closely similar to those reported in the literature for whole ascites cells and for a cell membrane preparation. Likewise, the fatty acid composition of phospholipids from the granules in general was similar to that reported for Ehrlich ascites cells. On the basis of the polar and neutral lipid ratio, the lipid granules of the ascites cells were calculated to possess lipid core diameters of 30-50 nm, which were 40-70 times smaller than those (up to 2 mu) measured for the lipid granules of the intact cells by electron microscopy. The characterization of the lipid composition of the Ehrlich ascites lipid granules was completed by determining the molecular species composition of the diacyl, alkylacyl and alkenylacyl phosphatidylethanolamines and of the diacyl and alkylacyl phosphatidylcholines of the ascites cells. It is concluded that the alkyldiacylglycerols of the Ehrlich ascites cells occur largely in the cytoplasmic lipid granules, which appear to consist of many particles of the size and structure of very low density lipoproteins enclosed in membranous sacs.

Fine-structural and morphometrical studies on the segmental septa of the giant fibers in the earthworm, Eisenia foetida

The fine structure of junctional specializations on the segmental septa in the median and lateral giant fibers of the earthworm (Eisenia foetida) was examined. Eight morphologically different septal domains were identified; a gap junction, a junction with hemispherical hollow structures, a chemical synapse-like junction, intermediate type and punctum adherens type junctions, a junction with adjoining vesicular layers, an area flanked by flattened membranous sacs, a non specialized area, and an area consisting of widely separated membranes with interposed glial processes. The area of each domain was measured by a cytometrical technique using quasi-serial sections. The gap junction occupied 3% and 0.2% of the septal area of the median and lateral giant fibers, respectively. Junctions with hemisperical hollow structures, characteristic of the earthworm giant fibers, occupied 2.5% and 13.9% of the median and lateral giant fibers, respectively. Various membrane domains except the gap junction, the junction with hemispherical hollow structures, and the chemical synapse-like junction accounted for similar proportional areas in both median and lateral giant fibers. The functional implications of these junctional specializations, especially the gap junction, are discussed.

Presynaptic effects of 4-aminopyridine and changes following a single giant impulse at the Torpedo nerve-electroplaque junction

The presynaptic changes caused by 4-aminopyridine were studied in the electric organ of Torpedo marmorata, in the resting state and during the period following transmission of a single giant discharge. Incubation with 4-aminopyridine provoked a 30–40% decrease in the density of synaptic vesicles in nerve terminals, and a similar decrease in the content of vesicular and free acetylcholine. These changes were not observed when 4-aminopyridine was applied in a low-calcium, high-magnesium solution. In the standard medium, 4-aminopyridine treated junctions were able to generate a giant electrical discharge of long duration in response to a single stimulus. During the seconds and minutes following the giant discharge, the number of synaptic vesicles was not found to be significantly altered in the whole population of nerve terminals. However, new membranous structures—looking like sacs with double membranes encircling a part of cytoplasm—were seen in approximately 25% of nerve endings; in those terminals, the number of synaptic vesicles was significantly decreased. At this stage, the junctions had not recovered their capability to generate a second giant discharge of full size and the yield of acetylcholine, adenosine 5′-triphosphate (ATP) and creatine phosphate was diminished. Thirty minutes after the single discharge, the functional recovery was achieved and the membranous sacs had disappeared; but the levels of acetylcholine, ATP and creatine phosphate were still not restored.

A unique case of abdominal pregnancy: What are the minimal requirements for placental contact with the maternal vascular bed?

In this report we describe a case of abdominal pregnancy in which the placenta engaged part of the wall of an intra-abdominal membranous sac with only minimal vascular connection with the peritoneal surface. A male infant weighing 3150 gm was delivered at 38 weeks' gestation. We believe this case represents the first report in the literature of an abdominal pregnancy without placental attachment to the maternal viscera.

Functional morphology of the cap‐like apparatus in autozooids of a Palaeozoic trepostome bryozoan

A membranous, cap-like structure was discovered in the bryozoan genus Hallopora from upper Ordovician siltstones from Sardinia. The structure is interpreted to be analogous to the perimetrical attachment organ and to the part of the membranous sac sustaining the sphincter muscle in Recent cyclostomes. The progressive mineralization of the cap-like apparatus occurred in later ontogenetic stages of the colony in order to have the function of a terminal diaphragm. This diaphragm is related to a particular degeneration—regeneration cycle very similar to the cyclic growth patterns (intracolony overgrowths) of some post-Palaeozoic cyclostomes. After this phase the colony seems to end its life cycle.