Cellular organization of the dome sensillum: A presumed chemoreceptor in Gammarus setosus (Gammaridea: Amphipoda)

A previously unknown type of sensillum with a thin cuticular dome and two pairs of pores is described in the amphipod Gammarus setosus. There is only one dome sensillum on each interantennal lobe of the head. The receptor is innervated by two sensory dendrites that bifurcate into two pairs of 9 + 0 cilia, concentrically enclosed by four auxiliary cells—two thecogen, one trichogen, and one tormogen and surrounded by a cluster of accessory cells. The ciliary regions are contained in small inner lymph cavities. The outer segments are sheathed by the apical extensions of the thecogen cells, are looped inside the outer lymph cavity, and come in close contact with lipid spheroids inside the dome. The basal bodies consist of microtubule doublets, which extend into the distal segments where they are interspersed with singlets. The nodal inner dendritic segments join the ventral suspension cord of the organ of Bellonci and enter its ganglion. The application of colloidal lanthanum resulted in intraciliary lanthanum deposits. The dome sensilla are presumed to be chemosensory because their cellular plan has similarities to that of some known olfactory and pheromone-sensitive sensilla in decapod crustaceans and insects. © 1994 Wiley-Liss, Inc.     

Morphology and ultrastructure of the organ of Bellonci in the marine amphipod Gammarus setosus

The three-dimensional structure of the organ of Bellonci in the marine amphipod Gammarus setosus and the relationship between its sensory cells and concretion are described using light, transmission, and scanning electron microscopy, with chemical treatment for cell lysis, calcium chelation, glycogen staining, and lanthanum labelling. The organ is encapsulated and has three units called fuselli. Each is enclosed by two fusellar cells which generate and release calcium granule strands into the cores of the fusellar concretions, which are united in the center of the organ. The surface of each fusellus is traversed by spiral dendrites entering dorsally and ending ventrally. The spiral dendrites arise from sensory neurons contained in a palm-shaped ganglion in the center of the capsule, beyond which they are twisted like a rope before reaching the concretion. The spiral dendrites are linked in pairs by gap and tight junctions and each gives origin to two pairs of 9+0 sensory cilia 30 μm apart. The ciliary distal segments give rise to long tubules which are in contact with the calcium granule strands. The ciliary proximal segments are expanded by many long mitochondria which interdigitate with the branched striated ciliary rootlets. The concretion is suspended in the capsule cavity by axons originating from four neurons of a remote mechanoreceptor. The structure of the organ suggests that it is a sensory organ involved in the reception and integration of a variety of stimuli.     

The ciliated epidermis of Xenoturbella bocki (Platyhelminthes, Xenoturbellida) with some phylogenetic considerations

The epidermis of Xenoturbella bocki Westblad was studied by scanning and transmission electron microscopy. Two cell types predominate in the epidermis: multiciliated epidermal cells and non-ciliated or monociliated gland cells. A conspicuous feature is the dense ciliary coverage and the numerous gland cell openings. Xenoturbella has a characteristic pattern of axonemal filament termination in the distal tips of their cilia. Each epidermal cilium has the typical 9 + 2 patten through the major part of its shaft. Near the tip there is a shelf at which doublets 4–7 terminate. Doublets 1, 2, 3, 8 and 9 continue into the thinner distal part of the cilium. A similar shelf in cilia is known only from the turbellarian orders Nemertodermatida and Acoela, and hence may be an apomorphic feature which indicates a close relationship between Xenoturbellida, Nemertoder-matida and Acoela. The basal body is provided with a so-called basal foot which has a cross-striated appearance and an expanded distal plate that seems to act as a microtubule organizing center. Approximately 15–25 microtubuli radiate from the endplate of the basal foot to the basal bodies caudally. The arrangement of basal foot and ciliary rootlets in Xenoturbella differs from that of Acoela and related orders in that there are two striated rootlets only (an anterior and a posterior one), rather than one main rootlet and two lateral rootlets.     

TEM studies on the lattice organs of cirripede cypris larvae (Crustacea, Thecostraca, Cirripedia)

 Lattice organs consist of five pairs of sensory organs situated on the dorsal carapace in cypris larvae of the Crustacea Cirripedia. The lattice organs in cypris larvae of Trypetesa lampas (Acrothoracica) and Peltogaster paguri (Rhizocephala) represent the two main types found in cirripedes, but only minor differences exist at the TEM level. Each lattice organ is innervated by two bipolar, primary receptor cells. The inner dendritic segment of each receptor cell carries two outer dendritic segments. The outer dendritic segments contain modified cilia with a short ciliary segment (9×2+0 structure). Two sheath cells envelop the dendrite except for the distal ends of the outer dendritic segments. This distal end enters a cavity in the carapace cuticle and reaches a terminal pore situated at the far end of the cavity. The cuticle above the cavity is modified. In both species the epicuticle is partly perforated by numerous small pores and the underlying exocuticle is much thinner and less electron dense than the regular exocuticle. Lattice organs very probably have a chemosensory function and are homologous with the sensory dorsal organ of other crustacean taxa. Accepted: 18 August 1998     

Ultrastructure of the proximal region of somatic cilia in Paramecium tetraurelia

The morphology of the transition zone between the terminal plate of the basal body and the 9 + 2 region of the somatic (non-oral) cilium has been examined in Paramecium tetraurelia. Freeze-fracture and thin- section techniques disclosed both membrane specializations and various internal structural linkages. Freeze-fracture material revealed sets of particles interrupting the unit membrane. The more distal of these form plaquelike arrays while the proximal set of particles forms the ciliary "necklace." The plaque regions correspond to anionic sites on the outer membrane surface as revealed by binding of polycationic ferritin. Both the plaque particles and the necklace particles appear to be in contact with outer doublet microtubules via a complex of connecting structures. In the interior of the transition zone an axosomal plate supports an axosome surrounded by a ring of lightly packed material. Only one of the two central tubules of the axoneme reaches and penetrates the axosome. Below the axosomal plate four rings, each approx. 20 nm wide, connect adjacent outer doublets. An intermediate plate lies proximal to these rings, and a terminal plate marks the proximal boundary of this zone. Nine transitional fibers extend from the region of the terminal plate to the plasmalemma. The observations described above have been used to construct a three-dimensional model of the transition region of "wild-type" Paramecium somatic cilia. It is anticipated that this model will be useful in future studies concerning possible function of transition-zone specializations, since Paramecium may be examined in both normal and reversed ciliary beating modes, and since mutants incapable of reverse beating are available.     

Fine structural localization of phosphatases in cilia and basal bodies of Tetrahymena pyriformis.

Cytochemical localization of ATPase activities in cilia and basal bodies of Tetrahymena pyriformis revealed a number of possible sites of ATPases. In basal bodies, reaction product was localized on the periphery of basal body microtubules, in the core of the B-microtubules, on the dense basal body core, and on the basal plate; some reaction product was associated with the postciliary and basal microtubules. In the cilium, reaction product was associated with the ciliary membrane, the basal granule, the periphery of the outer doublet microtubules, in the core of the B-microtubules, and on the arms and either the central microtubules or the radial spoke heads. Reaction product deposition required ATP and either Ca2+ or Mg2+ or ADP and Mg2+. When incubated in the presence of ATP and Na+, reaction product was only found at the base of the cilium in the region of the ciliary necklace. Implications of the various sites of activity are discussed with respect to possible mechanisms of ciliary motility.     

The fine structure of a cephalic sensory receptor in the copepod Doropygus seclusus Illg (Crustacea: Copepoda: Notodelphyidae)

A cephalic organ of presumed sensory function is described in nauplii and copepodids of the ascidicolous copepod Doropygus seclusus Illg. The receptor, located bilaterally in the anterodorsal head region, is composed of dendrites of extra optic protocerebral origin which have ciliary protrusions with basal bodies, no rootlets, and a basal infrastructure of the 9 + 0 type. The cilia do not branch and their distal terminations contain only one to four microtubules. In nauplii and free-living copepodids, a large epidermal supporting cell encapsulates the end of one dendrite and its cilia in a sac. Other dendrites and their cilia pass through the supporting cell and, terminally, the cilia escape to form a whorled fascicle which contacts the anterolateral cephalic cuticle. The latter end organ reaches its greatest development in the second copepodid stage — the stage which infects the ascidian. All of the symbiotic stages of the copepod have only a proportionately smaller end organ of the saccular type and apparently lack the end organ consisting of whorls of ciliary ends. The function of the receptor is unknown, but it is suggested that the end organ which disappears in the symbiotic stages functions in second copepodids in host recognition.     

Ultrastructure of gill cilia and ciliary rootlets of Chaetoderma nitidulum Lovén 1844 (Mollusca, Chaetodermomorpha)

Cilia and associated structures on the gill lamellae on the ctenidum of Chaetoderma nitidulum were studied. The gill cilia are very long and have a whip-like narrow portion distally, where only three microtubule doublets continue to the distal tip. In the transition zone between the cilium and the centriolar triplet section of the basal body there is a dense plate, an aggregation of granules and a ciliary necklace with four strands. Further down there is a short cross-striated basal foot and two conical cross-striated ciliary rootlets. The first rootlet is flattened and directed forward. It connects distally with the basal feet of other adjacent cilia. The second rootlet is rounded in cross-section and vertically directed. The epithelial structures of Chaetoderma show similarities with other Mollusca. We found no structural characters that could support the current hypothesis of a close relationship of Xenoturbella to the Mollusca.     

Bld10/Cep135 stabilizes basal bodies to resist cilia-generated forces

Basal bodies nucleate, anchor, and organize cilia. As the anchor for motile cilia, basal bodies must be resistant to the forces directed toward the cell as a consequence of ciliary beating. The molecules and generalized mechanisms that contribute to the maintenance of basal bodies remain to be discovered. Bld10/Cep135 is a basal body outer cartwheel domain protein that has established roles in the assembly of nascent basal bodies. We find that Bld10 protein first incorporates stably at basal bodies early during new assembly. Bld10 protein continues to accumulate at basal bodies after assembly, and we hypothesize that the full complement of Bld10 is required to stabilize basal bodies. We identify a novel mechanism for Bld10/Cep135 in basal body maintenance so that basal bodies can withstand the forces produced by motile cilia. Bld10 stabilizes basal bodies by promoting the stability of the A- and C-tubules of the basal body triplet microtubules and by properly positioning the triplet microtubule blades. The forces generated by ciliary beating promote basal body disassembly in bld10Δ cells. Thus Bld10/Cep135 acts to maintain the structural integrity of basal bodies against the forces of ciliary beating in addition to its separable role in basal body assembly.     

Organization of actin microfilaments in the apical border of oviduct ciliated cells

Actin microfilaments were localized in quail oviduct ciliated cells using decoration with myosin subfragment S1 and immunogold labeling. These polarized epithelial cells show a well developed cytoskeleton due to the presence of numerous cilia and microvilli at their apical pole. Most S1-decorated microfilaments extend from the microvilli downward towards the upper part of the ciliary striated rootlets with which they are connected. From the microvillous roots, a few microfilaments connect the proximal part of the basal body or the basal foot associated with the basal body. Microfilament polarity is shown by S1 arrowheads pointing away from the microvillous tip to the cell body. Furthermore, short microfilaments are attached to the plasma membrane at the anchoring sites of basal bodies and run along the basal body. The polarity of these short microfilaments is directed from the basal body anchoring fibers downward to the cytoplasm. At the cell periphery, microfilaments from microvillous roots and ciliary apparatus are connected with those of the circumferential actin belt which is associated with the apical zonula adhaerens. Together with the other cytoskeletal elements, the microfilaments increase ciliary anchorage and could be involved in the coordination of ciliary beating. Moreover, microvilli surrounding the cilia probably modify ciliary beating by offering resistance to cilium bending. The presence of microvilli could explain the fact that mainly the upper part of the cilia appanars to be involved in the axonemal bending in metazoan ciliated cells.     

A comparative study of ciliary differentiations in the branchial stigmata of ascidians

In a correlated thin sectioning and freeze-fracturing study, we have examined species belonging to the orders of the ascidian class: Stolidobranchiata (Botryllus schlosseri, Botrylloides leachi, Molgula socialis, Styela plicata), Phlebobranchiata (Ascidiella aspersa, Phallusia ingeria, Ciona intestinalis) and Aplousobranchiata (Clavelina lepadiformis). Though the branchial basket varies in the complexity and filtration efficiency in the three orders, the ciliated epithelia aroand the stigmata contain a common pattern of organization; seven rows of flattened cells, each bearing a single row of long cilia flanked by a single row of microvilli. All the species examined possess ciliary specializations represented by: (a) bridges connecting doublets number 5 and 6 as well as 9.1 and 2; (b) dense material lying between the above mentioned axonemal doublets (5-6 and 1-2) and the ciliary membrane, sometimes in the shape of longitudinal strands or often as lines of dots; (c) a fuzzy coat protruding from the ciliary membrane, consisting of tufts or scattered filaments; (d) intramembrane particles (IMPs) associated with the P-face of the membrane, often arranged in clusters and orderly alignments related to the anderlying axonemal doublets; these IMPs decorate the opposite sides of each cilium facing the adjacent cilia forming the ciliary rows of adjacent cells and are absent on the lateral sides. The stigmatal cilia propel water through the stigmata and their effective strokes follow a line at right angles to the row of cilia in each cell. The usual direction of the effective stroke is toward doublets 5-6. It is possible, therefore, to refer to structure in relation to the ciliary beat cycle. The importance of these specializations is unknown, but the structures appear to vary in the different species. A correlation between the richness of the specializations and the complexity of the branchial basket was not evidenced. It was suggested that the ciliary specializations relate to the peculiar organization of the stigmatal margin and that all are involved in the regulation of the ciliary activity.     

ULTRASTRUCTURAL ORGANIZATION OF CILIA AND BASAL BODIES OF THE EPITHELIUM OF THE CHOROID PLEXUS IN THE CHICK EMBRYO

Ultrastructural studies were performed on normal and abnormal cilia and basal bodies associated with the choroidal epithelium of the chick embryo. Tissues were prepared in each of several fixatives including: 1% osmium tetroxide, in both phosphate and veronal acetate buffers; 2% glutaraldehyde, followed by postfixation in osmium tetroxide; 1% potassium permanganate in veronal acetate buffer. Normal cilia display the typical pattern of 9 peripheral doublets and 2 central fibers, as well as a system of 9 secondary fibers. The latter show distinct interconnections between peripheral and central fibers. Supernumerary fibers were found to occur in certain abnormal cilia. The basal body is complex, bearing 9 transitional fibers at the distal end and numerous cross-striated rootlets at the proximal end. The distal end of the basal body is delimited by a basal plate of moderate density. The tubular cylinder consists of 9 triple fibers. The C subfibers end at the basal plate, whereas subfibers A and B continue into the shaft of the cilium. The 9 transitional fibers radiate out from the distal end of the basal body, ending in bulblike terminal enlargements which are closely associated with the cell membrane in the area of the basal cup. One or 2 prominent basal feet project laterally from the basal body. These structures characteristically show several dense cross-bands and, on occasion, are found associated with microtubules.     

Ciliary specializations in branchial stigmatal cells of protochordates

Tissues from the pharynx of five representative species of the protochordates (subphylum Tunicata, the three classes Ascidiacea, Thaliacea and Appendicularia, and subphylum Cephalochordata) were examined in both thin sections and freeze-fracture replicas. In all species, the stigmatal cilia of the branchial chamber are neatly arranged and move continuously to propel sea-water in a fixed direction for respiration and feeding of the organism. A number of specializations are found in the basal region of these cilia and are represented by: a) bridges connecting axonemal doublets numbers 5 and 6; b) dense fibrous material linking the doublet microtubules of the axoneme to the ciliary membrane, sometimes in the shape of longitudinal strands or as clusters of filaments; c) intramembrane particles (IMPs) associated with the P-face of the membrane, often arranged in clusters evenly aligned along the ciliary shaft in relation to the underlying axonemal doublets. Ciliary specializations are distributed along the plane of the effective stroke of the beat in both the ascidian Botryllus schlosseri and in the thaliacean Pyrosoma atlanticum and the amphioxus Branchiostoma lanceolatum, whereas in the thaliacean Doliolum nationalis and the appendicularian Oikopleura dioica a more uniform distribution of these specializations all around the basal portion of the cilia is observed. Whatever the disposition of the ciliary specializations in all the examined species, they are always present at the base of the water-propelling cilia. Some morphological evidence suggests that these specializations play a mechanical function in tethering the ciliary membrane to the axoneme. We propose that they help maintain the orientation of the cilia during beating, enhance their stiffness and improve their efficiency.     

Observations on the solitary cilium of rabbit oviductal epithelium: its motility and ultrastructure

Solitary cilia have been observed on rabbit oviductal epithelial cells. In tissue cultures of fimbrial epithelium of 3- and 4-day-old animals observed by phase microscopy, most of these single cilia exhibited a vortical or funnel-type movement while others had the usual to-and-fro motility. Primary cilia are usually considered immotile. Transmission electron microscopy of specifically identified single cilia revealed differences between the ciliary shafts and basal bodies of the single cilia as compared to those of mature oviductal ciliated cells. The basal body of the solitary cilium often had at least two triangular, striated, basal foot processes, lacked electron-dense satellite material around its basal end, and occasionally had striated rootlets. In contrast, the cilia of mature ciliated cells had only one basal foot, exhibited much electron-dense satellite material, and lacked rootlets. Cross sections of the single cilia showed patterns of microtubules different from the usual 9 + 2 axonemal complexes of normal cilia and included 9 + 0, 10 + 2 singlets, 7 + 2 doublets, and 8 + 1 doublet and 2 singlets; one did have the usual 9 + 2 arrangement. We postulate that the presence of more than one basal foot process may be responsible for the vortical motility observed. The primary cilia are shorter than normal cilia; the longest one measured was 1.86 micron in length, 0.28 micron in width at its base, and 0.14 micron at its tip. Based on the light-microscopic, scanning-electron-microscopic and transmission-electron-microscopic observations, such solitary cilia were observed more frequently in the oviductal tissues of the 3- to 4-day postnatal rabbits grown in tissue culture and in ovariectomized and ovariectomized/progesterone-treated adult animals than in estrous, ovulatory, or ovariectomized/estradiol-treated rabbits.     

Fine Structure and Function of Pharynx Cilia in Glossobalanus minutus Kowalewsky (Enteropneusta)

Two kinds of cilia have been observed in the pharynx of Glossobalanus minutus Kowalewsky. From the present study, a ciliary specialization can be found in order to move a determinate substance, i.e. mucus or water. Mucus-moving cilia (type I cilia) have a single basal centriole and poorly developed ciliary rootlets. Their tips are rounded, bearing an inner, asymmetrical cap attached to some tubules. Water-moving cilia (type II cilia) are exclusively located at lateral epithelia of branchial bars, giving rise to the water current through the gills. They have two basal centrioles, proximal and distal, and a complex system of ciliary rootlets made up of a principal rootlet, a secondary or accessory rootlet and a 'fan' rootlet. The tips of type II cilia have a long process with some tubules inside. All basal structures are precisely orientated in order to assure a good coordination of ciliary beat. The possible functional significance of ciliary substructure is also discussed. From these observations a model for mucus and water currents through gill slits is postulated.     

Development and enzyme activity of protein bodies in proteinoplasts of tobacco root cells

The development of protein bodies in proteinoplasts of tobacco (Nicotiana tabacum L. var. Wis. 38) roots was investigated with TEM, HVEM, and enzyme cytochemistry. These plastids contain a three-dimensional network of fenestrated tubules which originate from invaginations of the inner membrane of the plastid envelope. Elaboration of the network occurs in parallel with cell differentiation: slender tubules common to plastids in meristematic cells undergo dilation as protein accumulates during cell differentiation; proteinoplasts of vacuolate and root cap cells usually contain a large protein body. The contents of the peripheral tubules, originating from the inner membrane, are less electron dense than the tubules making up the central network. Localized dilations within the tubular network result in the formation of dense spheroidal structures, protein bodies, apparently as a result of continued protein accumulation via tubules connecting to the central network. Protein might be imported from segments of rough ER attached to or apposed to the outer membrane of the proteinoplast envelope. The presence of catalase (E.C. 1.11.1.6), peroxidase (E.C. 1.11.1.7), and cytochrome oxidase (E.C. 1.9.3.1) was demonstrated by cytochemistry with diaminobenzidine (DAB) as substrate. Oxidized DAB was found in protein bodies after incubation in each of the specific reaction media. While aminotriazole and sodium azide inhibited oxidation of DAB by catalase and peroxidase, respectively, only potassium cyanide completely inhibited oxidation of DAB in protein bodies. We conclude that protein bodies of proteinoplasts in tobacco roots are not sites for storage of protein, rather protein bodies contain heme protein(s) with strong oxidase activity that may convey a specific function to proteinoplasts.     

Biogenesis of the ciliary roots: participation of the dictyosomes of Golgi's complex.

In this study, the hypothesis of a possible biogenesis of the ciliary roots is suggested, after observing the cilia neurons under the electron microscope, which were found as an exception in the periaqueductal nucleus of the mesencephalon in the domestic cat, conserving the potential to differentiate the cilia, basal bodies and ciliary roots. The dictyosomes of Golgi's complex and Golgi's vesicles participated in this biogenesis. Vesicles of approximately 71.6 nm in diameter had become separated from the periphery of the flattened discoid cisterns of the dictyosome and were aligned normally, in tangential contact with each other, forming rows of vesicles or 'ringed chains', whose points of contact formed the beginning of the 'periodic striation' of a thin ciliary root. Later, the lateral walls of the vesicles and the molecules of the intracisternal proteins gave rise to the interperiodic microfilaments, when the carrier proteins were transformed into structural proteins of the ciliary roots. The parallel apposition of several ringed chains or thin ciliary roots, with their rings joined at the same level (or transversal striations), gave rise to thicker striated roots. This hypothesis of an ultrastructural biogenesis of the striated ciliary roots involves the following six stages: stage I = separation of Golgi's vesicles from the periphery of the flattened disk of dictyosomes near the basal body, with a diameter of over 71.6 nm; stage II = reinforcement of the membrane of the vesicles at the two opposite polar ends of its larger diameter; stage III = alignment of vesicles to form ringed chains, due to the tangential contact between their reinforced points; initiation of the 71.6-nm striation period, roots ringed linearly; stage IV = formation of joining microfilaments between periods (69.2 nm) with the lateral walls of the vesicles and the molecules of the proteins in their content; stage V = lengthening of the thin ciliary roots due to the coupling of new Golgi's vesicles at their ends so that their length increases as a result of the addition of terminal vesicles; stage VI = increase in thickness of the thin ciliary roots, due to the parallel apposition of several ringed chains or thin ringed ciliary roots, at the point where their transversal striation points coincide.     

Gradients of proliferation of ciliary basal bodies and the determination of the position of the oral primordium in Tetrahymena.

The pattern of proliferation of new basal bodies in ciliary rows (somatic proliferation) in Tetrahymena was observed. Starved and refed cells were used, because proliferation in these cells is more pronounced than that under other circumstances. The formation of new basal bodies is locally determined by the position of "old" pre-existing basal body (short range determination). However, the probability of proliferation associated with any given "old" basal body differs very much. This probability is determined by the spatial coordinates of the particular region of the cell (long range determination); however some randomness in this process was also observed. Two different gradients of proliferation were found. The first gradient is circumferential with a maximum number of new basal bodies added in ciliary rows n, 1, 2 and 3 and the minimum number added in ciliary rows 7, 8 and 9. The second is an antero-posterior gradient with the highest number of new basal bodies added in the midbody region. Moreover, at least in some cases, new oral primordia first appear, as a random proliferation of new basal bodies adjacent to a few old cilia of ciliary row No. 1, resembling somatic proliferation. Then 2,3 or even more clumps of basal bodies appear, each having one old cilium posteriorly. These clumps, however, are not linear groups within the ciliary row but instead they form small fields of basal bodies. These findings suggest, that the same two-gradient system for new basal body addition operates during somatic proliferation and also determines the position of the new oral primordium as the site of the highest gradient value at the intersection of two gradients.     

Muciliary transport in newt lungs: the ultrastructure of the ciliary apparatus in isolated epithelial sheets and in functional triton-extracted models

High voltage and conventional electron microscopy were used to investigate the ultrastructure of the ciliary apparatus in intact and in Triton-extracted, reactivated sheets of mucociliary epithelium isolated from newt lung. Each long (about 13 microns) ciliary axoneme terminates on a barrel-shaped basal body which is anchored in the apical cytoplasm by a variety of accessory structures. A basal foot is associated with the midpoint of each basal body and acts as a focal point for numerous microtubules (MTs). In many cases MTs can be seen to interconnect the feet of neighbouring basal bodies. Attached to the proximal end of each basal body and extending in a direction opposite the basal foot is a large 'ciliary root'. Each ciliary root is associated with a distinct bundle of 6-7 nm microfilaments which appear to stain with the specific F-actin probe NBD-phallacidin. A single 3-4 microns long striated rootlet inserts into each ciliary root and extends toward the cell nucleus through an extensive network of microfilaments. At the level of the basal plate 'Y-shaped' structures appear to connect each axonemal outer doublet MT to the plasma membrane. All of these ciliary accessory structures are present in the same relationship in Triton-extracted models. Their morphology and distribution indicates that they serve to anchor the cilia in the apical cytoplasm. In addition some of these structures appear to be responsible for maintaining the structural and functional integrity of the ciliary field in the demembranated and reactivated models.     

A re-evaluation of the cytology of cat Pacinian corpuscles

Summary The aesthetascs of the spiny lobster, Panulirus argus, are hair sensilla located on the lateral filaments of the antennules. Each hair is about 0.8 mm long and innervated by about 320 bipolar sensory neurons, the dendrites of which project as a bundle into the hair shaft. Each of the dendrites develops two cilia. Within a very short distance each of these cilia branches repetitively and dichotomously resulting in 8000 to 10000 outer dendritic segments per hair, or about 20 to 30 branches per neuron. The branches intertwine frequently before running to the tip of the hair. Each hair also possesses inner and outer auxiliary cells. The inner auxiliary cells surround the bundle of dendrites, extending distally to the origin of the ciliary segments. Extensions of these cells project into the bundle of dendrites, separating groups of dendrites into discrete clusters. Outer auxiliary cells wrap the inner ones, but do not extend beyond the base of the hair.