Ciliary Segment Research Articles

Tangential Scleral Myopexy (TSM) as an Alternative to Muscle Resection in Strabismus Treatment

To present the new method as a variant of minimal invasive strabismus surgery (MISS) technique for less invasive and faster reсtus muscle plication. Extraocular muscle strengthening is common for strabismus treatment. Plication as an alternative for tightening or strengthening muscles appears to be less traumatic, quicker and vascular preserving operation. A new plication variant performed by fixating the edge of muscle with 6-0 vicril sutures and pulling them forward and oversewn at 2–3 mm from external part sclera-tendon joint avoiding the anterior ciliary artereies. The distance of muscles advancement depends on the eye deviation angle and calculated by Kenneth Wright charts. In all patients fornix transconjunctival access was performed. Proposed trapezoidal scleral myopexy (TSM) was performed in 26 patients at the age from 3 to 32 years old (children 3–15 y.o. = 29; adults 20–32 y.o. = 7). 23 consecutive patients underwent TSM combined with antagonist recession at the same eye (15 esotropia, 11 exotropia). Follow up period was 6–26 months. The results were considered satisfactory if the postoperative angle was between 0 ± 3° (92.3 %). Only 2 cases (7.6 %) failed to reach this standart. The obtained results considered as very satisfactory. Patients reported only minimal postoperative discomfort and no complain on cosmetics. Trapezoidal muscle plication was inconspicuous throught the conjunctive. The good results of TSM proposed by the author seems to be very simple and more effective for muscle strengthening comparing to resection of medial and lateral rectus muscles. Placement of sutures at the muscle edge during trapezoidal plication exclude ciliary vassel destruction and anterior segment ischemia. The obtained results demonstrated that TSM was considered to be equivalent to resection of horizontal rectus and especially of vertical rectus muscles. Trapezoid form of plication increases the arc of sclera contact to the muscle, probably, explaining the efficiency of proposed operation for muscle strengthening. Proposed modification of muscle plication is reversible, simple, sparing for ciliary artery procedure and is recommended as minimal invasive strabismus surgery (MISS) for simultaneous operation on multiple rectus muscles.

Time-Lapse Live-Cell Imaging Reveals Dual Function of Oseg4, Drosophila WDR35, in Ciliary Protein Trafficking.

Cilia are highly specialized antennae-like organelles that extend from the cell surface and act as cell signaling hubs. Intraflagellar transport (IFT) is a specialized form of intracellular protein trafficking that is required for the assembly and maintenance of cilia. Because cilia are so important, mutations in several IFT components lead to human disease. Thus, clarifying the molecular functions of the IFT proteins is a high priority in cilia biology. Live imaging in various species and cellular preparations has proven to be an important technique in both the discovery of IFT and the mechanisms by which it functions. Live imaging of Drosophila cilia, however, has not yet been reported. Here, we have visualized the movement of IFT in Drosophila cilia using time-lapse live imaging for the first time. We found that NOMPB-GFP (IFT88) moves according to distinct parameters depending on the ciliary segment. NOMPB-GFP moves at a similar speed in proximal and distal cilia toward the tip (~0.45 μm/s). As it returns to the ciliary base, however, NOMPB-GFP moves at ~0.12 μm/s in distal cilia, accelerating to ~0.70 μm/s in proximal cilia. Furthermore, while live imaging NOMPB-GFP, we observed one of the IFT proteins required for retrograde movement, Oseg4 (WDR35), is also required for anterograde movement in distal cilia. We anticipate our time-lapse live imaging analysis technique in Drosophila cilia will be a good starting point for a more sophisticated analysis of IFT and its molecular mechanisms.

Identification and expression patterns of two TRPV channel genes in antennae and Johnston's organ of the dengue and Zika virus vector mosquito, Aedes aegypti

Transient Receptor Potential (TRP) channels respond to diverse stimuli and function as primary regulators of sensory information such as olfaction and auditory. TRP proteins are activated by several chemicals and secondary messengers to modulate communications between cell to cell as well as to recognize some environmental changes. Here we report on the identification and localization of the Aedes aegypti homolog of the TRPV channel proteins that is conserved to other insect species based on comparison of amino acids sequences similarities. Transcripts of two TRPV proteins homologous to Drosophila TRPV proteins (Nan and Iav) were ubiquitously expressed in the whole tissues such as antennae, maxillary palps, proboscis, legs, and body of the mosquito. Indeed, TRPV channel family members were localized in sensilla chaetica and sensilla basiconica on the antennae as well as ciliary segment of Johnston's organs. Taken together, we infer that TRPV channels of Aedes aegypti may function as both a sound sensor involved in detection of sound signals and as a chemical sensor responding attractants or repellent compounds allowing them to respond to the appearance of predators or other environmental chemical cues at a distance with behaviors crucial for survival.

The Johnston's organ of three homopteran species: A comparative ultrastructural study

A transmission electron-microscopy study has been carried out on the pedicel of three homopteran species, with particular focus on the leafhopper Scaphoideus titanus Ball. The two other species, the planthoppers Hyalesthes obsoletus Signoret and Metcalfa pruinosa Say, were investigated in order to compare the ultrastructure of the Johnston's organ (JO) among representatives of the Auchenorrhyncha group. The results showed the presence of a well developed JO located within the pedicel. Depending on the species the JO is made of 25 up to 72 scolopidia arranged in a coronal array. Each scolopidium is connective, heterodynal, amphinematic and hosts three structurally dissimilar sensory neurons. Two of them have a type 1 ciliary segment while the third bears a type 2 cilium. The type 2 dendrite tip is associated with a tubular cap and is longer than the others, ending into the cuticle at the base of the flagellum. Other scolopidia with one or two neurons were found in S. titanus, forming an accessory organ. The presence of such a well developed mechanosensory apparatus is discussed in relation with the lifestyle of the three species.

Ciliogenesis in Caenorhabditis elegans requires genetic interactions between ciliary middle segment localized NPHP-2 (inversin) and transition zone-associated proteins

The cystic kidney diseases nephronophthisis (NPHP), Meckel–Gruber syndrome (MKS) and Joubert syndrome (JBTS) share an underlying etiology of dysfunctional cilia. Patients diagnosed with NPHP type II have mutations in the gene INVS (also known as NPHP2), which encodes inversin, a cilia localizing protein. Here, we show that the C. elegans inversin ortholog, NPHP-2, localizes to the middle segment of sensory cilia and that nphp-2 is partially redundant with nphp-1 and nphp-4 (orthologs of human NPHP1 and NPHP4, respectively) for cilia placement within the head and tail sensilla. nphp-2 also genetically interacts with MKS ciliopathy gene orthologs, including mks-1, mks-3, mks-6, mksr-1 and mksr-2, in a sensilla-dependent manner to control cilia formation and placement. However, nphp-2 is not required for correct localization of the NPHP- and MKS-encoded ciliary transition zone proteins or for intraflagellar transport (IFT). We conclude that INVS/NPHP2 is conserved in C. elegans and that nphp-2 plays an important role in C. elegans cilia by acting as a modifier of the NPHP and MKS pathways to control cilia formation and development.

Atlas of olfactory organs of Drosophila melanogaster: 2. Internal organization and cellular architecture of olfactory sensilla

Antennae and maxillary palps of Drosophila melanogaster were studied with the electron microscope on serial sections of cryofixed specimens. The number of epidermal cells roughly equals the number of sensilla, except for regions where the latter are scarce or absent. Each epidermal cell forms about two non-innervated spinules, a prominent subcuticular space and a conspicuous basal labyrinth, suggesting a high rate of fluid transport through the sensory epithelium. The internal organization and fine structure of trichoid, intermediate and basiconic sensilla is very similar. Receptor cell somata are invested by thin glial sheaths extending distad to the inner dendritic segments. Further distally, the thecogen cell forms a sleeve around the dendrites, but an extracellular dendrite sheath is absent. At the base of the cuticular apparatus, the inner sensillum-lymph space around the ciliary and outer dendritic segments is confluent with the large outer sensillum-lymph space formed by the trichogen and tormogen cells. All three auxiliary cells exhibit many features of secretory and transport cells but extend only thin basal processes towards the haemolymph sinus. The bauplan and fine structure of coeloconic sensilla differs in the following aspects: (1) the ciliary segment of the dendrites is located deeper below the base of the cuticular apparatus than in the other sensillum types; (2) a prominent dendrite sheath is always present, separating inner and outer sensillum-lymph spaces completely; (3) the apical microlamellae of the auxiliary cells are more elaborate, but free sensillum-lymph spaces are almost absent; (4) there are always four not three auxiliary cells. Morphometric data are presented on the diameter of inner and outer dendritic segments and on the size of receptor cells, as well as of the receptor and auxiliary cell nuclei. The special fine structural features of Drosophila olfactory sensilla are discussed under the aspects of sensillar function and the localization of proteins relevant for stimulus transduction.

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.

Proliferation of microtubules from discrete electron-dense bodies in the ciliary dendritic portion of mechanosensory setae of copepod antennae

Sensory setae on the appendages of most arthropods contain microtubules in their innervating dendrites. Both mechano- and chemoreceptors are of ciliary origin. Mechanoreceptive dendrites typically contain more microtubules than do chemoreceptive dendrites, perhaps reflecting a role for microtubules in stiffening the setae. The presence of microtubules may also increase the sensitivity of mechanotransduction.The overall arrangement of calanoid copepod mechanoreceptors has been described elsewhere. In calanoid copepods the arrangement of microtubules in the distal ciliary segment of the dendrites is dramatic: as many as 3000 microtubules per dendrite are found in parallel rows (fig. 1,3a). These bundles of microtubules extend some distance into the setae themselves. The basal bodies within these dendrites are especially electron-dense and give rise to a circlet of 9 + 0 microtubules (fig. 2,3f)- Just distal to the circlet electron-dense material begins to form adjacent to the microtubules (fig. 3e), eventually forming elongate electron-dense bodies radiating outward (fig. 3d).

Ultrastructural localization of 5'AMP odorant receptor sites on the dendrites of olfactory receptor neurons of the spiny lobster

A unique probe--biotinylated adenosine-5'-monophosphate (5'AMP-biotin)--was used in transmission electron microscopic (TEM) studies to localize 5'AMP odorant binding sites on the dendrites of olfactory receptor neurons in the aesthetasc sensilla of the spiny lobster, Panulirus argus. This probe is capable of both binding to and exciting 5'AMP-sensitive olfactory receptor neurons, as revealed through biochemical and electrophysiological assays. TEM studies showed that 5'AMP-biotin binding sites are distributed along the entire dendritic region that is exposed to odorants, including the transitional zone (between the inner and outer dendritic segments, including the ciliary segment) and all of the outer dendritic segment. The density of 5'AMP binding sites per micron2 of membrane is similar along the length of the olfactory dendrite. However, the relative number of 5'AMP-biotin binding sites per micron2 of sensillar area diminishes in the distal 30% of the aesthetasc due to a decrease in the amount of dendritic membrane in that region. The distribution of these 5'AMP binding sites is therefore much more extensive than that of enzymes that inactivate 5'AMP--5'ectonucleotidase/phosphatase--which are restricted to the transitional zone (Gleeson et al., 1991). Taken together, these results suggest that 5'AMP-biotin is labeling 5'AMP-specific olfactory receptor sites that are located along the entire outer dendritic segment and that can be coupled to olfactory transduction. This study represents the first in situ localization of specific olfactory receptor sites using a specific, functionally defined ligand.

Ultrastructure of a possible new type of crustacean cuticular strain receptor in Carcinus maenas (crustacea, decapoda).

A hitherto unknown sensillum type, the "intracuticular sensillum" was identified on the dactyls of the walking legs of the shore crab, Carcinus maenas. Each sensillum is innervated by two sensory cells with dendrites of "scolopidial" (type I) organization. The ciliary segment of the dendrite is 5-6 μm long and contains A-tubules with an electron-dense core and dynein arm-like protuberances; the terminal segment is characterized by densely packed microtubules. The outer dendritic segments pass through the endo- and exocuticle enclosed in a dendritic sheath and a cuticulax tube (canal), which is suspended inside a slit-shaped cavity by cuticular lamellae. The dendrites and the cavity terminate in a cupola-shaped invagination of the epicuticle. External cuticular structures are lacking. Three inner and four to six outer enveloping cells are associated with each intracuticular sensillum. The innermost enveloping cell contains a large scolopale that is connected to the ciliary rootlets inside the inner dendritic segments by desmosomes. Scolopale rods are present in enveloping cell 2. Since type I dendrites and a scolopale are regarded as modality-specific structures of mechanoreceptors, and since no supracuticular endorgan is present, the intracuticular sensilla likely are sensitive to cuticular strains. The intracuticular sensilla should be regarded as analogous to insect campaniform sensilla and arachnid slit sense organs.

Depolarization‐controlled parameters of the ciliary cycle and axonemal function

AbstractDepolarization‐induced cycles of a frontal cirrus of Stylonychia were investigated by applying methods of axial‐view analysis of the cilia, high‐speed microcinématography, and step voltage‐clamp. Rising depolarization (from 3 mV to 7ge; 30mV) increased the rate of beating from zero to maximally 58 Hz. During cyclic activity, the axis of the beat cone of a proximal segment of the cirrus was inclined by 60° (0° = perpendicular to cell surface), and was always oriented 90° counterclockwise to the power stroke. With the stimulus amplitude rising, the orientations of the power stroke and inclination were increasingly shifted in more counterclockwise directions by up to 80° After correction for inclination ( = normalization), and following planification of the track of the segment, we determined the following properties of the cycle during depolarization: The course of the cycle tended to be rounded, i.e., the ratio of major over minor amplitudes (= spatial polarity) approximated a value of 1.6 which is only two thirds of maximal spatial polarity observed during hyperpolarization. The angular velocity generally increased with rising steps of depolarization; up to +5 mV (and comparable to hyperpolarization‐induced responses), the velocity maximum occurred during the return stroke. With depolarizations ≥7 mV the angular velocity maximum shifted to the power stroke so that the temporal polarity (rates of power stroke over rates of return stroke) increased from 0.4 to 1.6. Calculations of the angular velocity as referred to the proximal ciliary segment level suggest active sliding rates (between 5 and 30 nm/ms) of identified pairs of doublet microtubules. Ciliary frequency is a function of the rate of reorientation of the cyclic track; this parameter, which corresponds to the rate of translocation of active sliding between pairs of doublets, grew with the amplitude of depolarization. Translocation rates were high during transitions between the beat phases (power stroke, return stroke), and were reduced during these phases. Orientational polarograms of the mean rates of both active sliding and sliding translocation show properties of discreteness as well as continuity. The depolarization‐induced changes in inclination, and the inferred patterns of sliding rate and sliding translocation rate, are compared with previous results from hyperpolarization‐dependent activation of the same motor organelle.

The ciliary cycle during hyperpolarization-induced activity: an analysis of axonemal functional parameters.

Motor responses of the frontal cirri of the ciliate Stylonychia were recorded at the axial view of the ciliary base with high-speed cinematography. Voltage-clamp applying sustained hyperpolarizing voltage steps was used to explore the properties of the ciliary cycle modulated by the membrane potential. Upon hyperpolarization between -1 and -13 mV, a previously inactive frontal cirrus reoriented from a neutral posture and started beating so that the axis of the beating cone of a proximal cirral segment assumed an orientation near 100 degrees (proceeding counterclockwise from posterior = 0 degrees) and inclination near 60 degrees (0 degrees = perpendicular to the cell surface). The major beating amplitude was limited to about 150 degrees. Increasing hyperpolarization increased the spatial polarity of the cycle (ratio of major over minor amplitude, from 2 to 2.4). Rates of the power stroke increased with hyperpolarizations up to -4 mV but were consistently smaller than those of the return stroke during the ciliary cycle (ratio: 0.4 to 0.6; = temporal polarity). Comparison of different hypothetical beat forms (0-shape, D-shape, and egg-shape) showed that the orientation-time data are the major determinants of the angular velocity and rate of reorientation of the cilium during the cycle. Geometric transformation of these data led to descriptions of the cycle of a proximal ciliary segment in terms of active sliding velocities and rates of unidirectional sliding translocation between identified doublets. Three voltage-sensitive functional parameters of the cilium--the inclination (which is noncyclic) and the rates of active sliding and sliding translocation (both of which are cyclic in nature)--are discussed as generating the spatial and temporal properties of the ciliary beat.

Structural and functional properties of the mechanoreceptors and chemoreceptors in the anterior oesophageal sensilla of the crayfish, Astacus astacus

The anterior oesophageal sensilla (AOS) of Astacus astacus are short cuticular cylinders with a terminal pore. Three sensory cells belong to each AOS, two of them having a dendritic ciliary segment of about 2 μm length (A-cells), the third having this segment about 12 μm long (B-cell). The ciliary A-tubules in the B-cells only possess arms and an electron-dense core. The dendritic inner segments of the A-cells terminate 3–6 μm distal of the B-cells. The dendritic tips of most A-cells are connected by desmosomes. All dendritic inner segments contain a ciliary rootlet and are accompanied by a scolopale within the innermost enveloping cell. There are four enveloping cells, three of which form thin subepithelial columns together with the enclosed sensory cells. Recordings from the posterior branch of the anterior oesophageal nerve containing the axons of the AOS revealed the presence of three types of sensory cells, two being chemosensitive and one mechanosensitive. One chemoreceptor is specifically sensitive to nicotinamide, but responded also to β-NAD, 6-aminonicotinamide, nicotinamide methyl esther and nicotin. It was blocked by p(4)-acetylpyridine. The second chemoreceptor responded only to crayfish gastric fluid. The mechanoreceptors reacted to stretch of the oesophageal wall adapting only slowly to maintained stimuli. It is assumed that the A-cells are the chemosensitive cells and the B-cells the mechanosensitive ones. The latter show only a small number of modality-specific characteristics. Several structural features appear to be correlated with the location of the AOS within a flexible surface, which undergoes considerable dilation.

Fine structure of sensilla on the ovipositor of the tephritid fly Urophora affinis

There are four types of sensilla on the ovipositor blade of Urophora affinis Frauenfeld, one more than was observed on three other species of fruit flies studied by other authors. Three of the types, uniporous gustatory pegs, campaniform organs, and tactile short hairs are common to the four species and generally are in similar positions on the blade. The fourth, uniporous gustatory plates, were noted in U. affinis only. The chemosensilla are innervated by three chemosensory dendrites that terminate below the pore and a mechanosensory dendrite with a tubular body that is attached to a basal cuticular apodeme of the covering cuticle. The dendritic tubular bodies of the campaniform organs and tactile hairs terminate parallel to the surface in a right-angular bend, where they are attached to basal apodemes of the covering cuticle. The chemosensilla and tactile hairs have individual outer and inner sheath cells, but the campaniform organs have individual inner sheath cells only. The part of the ciliary dendritic segment that is encased by the dendritic sheath passes through an epidermal cell, often with several sensilla sharing the same epidermal cell in place of an outer sheath cell. The role of these sensilla during oviposition is discussed.

Are the funnel-canal organs the 'campaniform sensilla' of the shore crab, Carcinus maenas (Decapoda, Crustacea)? II. Ultrastructure.

The funnel-canal organs on the dactyls of the shore crab, Carcinus maenas, are innervated by 3-24 sensory cells with unbranched dendrites, which attain a length of 500-1400 micron. The outer dendritic segments are enclosed in a dendritic sheath and pass through the cuticle within a canal. Two dendrite types can be distinguished according to ultrastructural criteria: Type I has a long ciliary segment, A-tubules with an osmiophilic core and arms, and a thick ciliary rootlet. Type II possesses only a short ciliary segment and a thin ciliary rootlet. Each funnel-canal organ contains two type-I dendrites. Their ciliary bases appear a few micron distal to those of the type-II dendrites (1 to 22 in number). Two inner and two to eight outer enveloping cells belong to a sensillum. The innermost enveloping cell contains a large scolopale. In the second enveloping cell single scolopale rods are present. Thus, the funnel-canal organs are characterized by structural features typical for mechanosensitive scolopidia, on the one hand, and for chemoreceptors, on the other. Therefore, the funnel-canal organs are very likely bimodal sensilla (contact chemoreceptors). A comparison with other arthropod sensilla shows that cuticular mechanoreceptors of aquatic crustaceans generally exhibit a 'scolopidial' organization.

Ultrastructure of the sensory palps ofTetranchyroderma papii (Gastrotricha, Macrodasyida)

The sensory palps of the macrodasyoid gastrotrichTetranchyroderma papii contain processes from two types of cell: 22–23 bipolar primary sensory cells and two to three support cells. In the proximal region of the palp each sensory cell contains a short ciliary segment with a basal body and from this ciliary segment a longer distal segment lacking axonemal microtubules extends through the major part of the length of the palp. Each support cell process bears microvilli and contains a conspicuous bundle of microtubules running the entire length of the process. The cell bodies of both cell types are situated in the epidermis of the head region. The palps are interpreted as having a chemosensory function. They are considered to be homologous to the posterior cephalic sensory organ ofTurbanella cornuta, but not the head tentacles ofChordodasys antennatus or nematode amphids.

Cryofixation without cryoprotectants. Freeze substitution and freeze etching of an insect olfactory receptor

Antennae of the silk moth, Bombyx mori, were frozen by immersion into propane at − 180 °C, and further processed by (a) freeze substitution (FS) or (b) freeze etching (FE). Although no cryoprotectant was used, freezing damage was observed in deeper tissue regions only. Data from FS specimens closely resemble those from FE replicas. Therefore, FS usually does not induce noticeable secondary artefacts by the preparation steps subsequent to freezing. When compared with chemically fixed antennae, the superior quality of cryofixation in this tissue is evident, particularly where cell surfaces and processes border the receptor lymph cavity: membranes are smooth following a steady course; dendrites and axons are round in cross-section with evenly distributed microtubules. The value of cryofixation is discussed with special reference to structures of presumed functional significance (e.g. stimulus conducting pore tubules, intramembrane particles of the receptor membrane, the ciliary segment of the dendrites, intercellular dilations, membrane junctions).

Ultrastructure of anterior sensory organs of the root-knot nematode, Meloidogyne incognita

Second-stage larvae of Meloidogyne incognita were examined to determine the ultrastructure of the labial, cephalic, and accessory sensory organs. The labial organs occur on the external surface of the nematode as six pores that encircle the stoma opening. Internally, each pore is surrounded by a cuticular canal containing receptors that consist of two modified cilia. Each cilium is an anterior extension of an axon. These axons collectively form nerve bundles and extend posteriorly to the nerve ring. An extracellular space surrounding each ciliary segment is continuous with a similar space formed by a laminar membrane complex that extends posteriorly within hypodermal tissue. The cephalic sensory organs, which are peripheral to the labial organs, lie in the two subventral and two subdorsal sectors of the anterior region of the nematode. These structures, whose organization resembles that of the labial organs, are innervated by modified cilia that are anterior extensions of axons, limited by canals, surrounded by the hypodermal tissue, and associated with adjacent membrane complexes. However, in contrast to the structure of a labial organ, each cephalic receptor is innervated by a single axon whose canal terminates beneath the cuticle of the nematode. A number of less clearly defined accessory axons occur in the anterior region of the nematode. These receptors, which are not enclosed by a canal, terminate beneath the cuticle of the nematode. Observations pertaining to the cuticular pores associated with labial organs indicate that these receptors may have a chemoreceptive or secretive function, whereas the lack of cuticular openings associated with the cephalic and accessory receptors suggests that these latter structures may be tactoreceptive.

Ultrastructure of the antennal sensilla of Acetes (Crustaces, Decapoda, Natantia, Sergestidae).

Many mesopelagic shrimps, including all Sergestidae and some Penaeidae, have long second antennae with similar patterns of setation. The morphology of the antenna and the ultrastructure of five types of antennal setae of the sergestid Acetes sibogae australis are described. The basal portion of the antenna of Acetes is normally held at about right angles to the long axis of the body; the antenna has a right-angle bend about a third of the way along its length and its distal two-thirds trails parallel to the body as the animal swims. Distal to the flexure each antennal segment bears a pair of type 1 setae, which bear lateral setules forming an almost closed tube on the medial side of the antenna. Although they have elaborate tracts leading from them, we believe that the type 1 setae are uninnervated. Two kinds of type 2 setae project into the lumen of the tube formed by the type 1 setae; thick type 2B setae have abundant setules nearly occluding the lumen of the tube and occur only just beyond the flexure; thin type 2A setae have fewer setules and occur at widening intervals along the full length of the tube. Both kinds are innervated by four neurones, three of which bear a ciliary dendrite, one a paraciliary dendrite. These four dendrites lose their microtubular structure proximal to the setal base but the tubule containing their amorphous extensions is fastened to the base of the seta by an amorphous electron-dense material. Both kinds of type 2 setae have a well-developed scolopale and are almost certainly mechanoreceptors. The proximal portion of the antenna bears four types of setae. Type 3 setae are paired, unadorned cylinders with a pore at the tip; although externally similar the type 3 A setae are innervated by three dendrites and the type 3 B by eight to ten. The dendrites of both 3 A and 3B setae have a short ciliary segment and poorly developed scolopales. Type 3 setae are probably chemoreceptors. A single setule-bearing type 4 seta occurs at the distal end of each segment of the basal third of the antenna closely associated with a pair of type 3 setae. Type 4 setae are innervated by three neurones each bearing a ciliary dendrite. These dendrites fuse distally and are attached to the wall of the seta at its base by dense amorphous material. Type 4’s have a well-developed scolopale and are probably mechanoreceptors. Type 5 setae are setule bearing, located on the posterior side of the antenna, and larger than the type 4’s, but their internal structure is identical to that of the type 4’s and they are also presumed mechanoreceptors. There are four to seven pairs of sparsely setuled type 6 setae found only within the antennal flexure and paired, setule-bearing type 7 setae are located at the tip of the antenna. Both types are presumed mechanoreceptors but their ultrastructure was not investigated. Literature on the ultrastructure of crustacean sensilla is summarized and compared with the results of the present study. Setal function and arrangement are then discussed in terms of the known behaviour and ecology of sergestids.

Labellar chordotonal organs of the mosquito, Culiseta inornata (Williston) (Diptera : Culicidae)

One chordotonal organ innervated by 2 bipolar neurons is found in each labellar lobe of the mosquito Culiseta inornata. Each chordotonal organ is connected by an attachment cell to the distal apex of each labellum. The axons of the chordotonal neurons form the core around which the sensory axons of chemosensory hairs coalesce to form the labial nerve. Nine pairs of neurotubules are found in the distal or ciliary segment of the dendrites. The proximal portion of the dendrites contains the ciliary collar, basal body and axial filament. The axial filament extends proximally to the nerve cell body and lies parallel with the nucleus. The chordotonal organs may act as proprioceptors sensing the amount of spreading of the labellar lobes during feeding.