Structure of the subgenual organ in the green lacewing, Chrysoperla carnea

REM and TEM studies of the subgenual organ in Chrysoperla carnea (Neuroptera: Chrysopidae) show that it is composed of three scolopidia, each with one sensory, one scolopale and one cap cell. The distal part of the dendrite shows a cilium with a '9 + 0' structure. The cross-handing pattern of the ciliary root has a periodicity of bands of about 61 nm. The scolopale material in a certain part of the scolopale cell is organized into five rods. The cell bodies of all three cap cells form a lens-like structure. the velum, which is fixed to the leg wall and the trachea with an extracellular material. The importance of the velum is discussed. Four types of intercellular junction are found; spot desmosomes. belt desmosomes, septate junctions and gap junctions.     

Structure of the auditory system of the weta Hemideina crassidens (Blanchard, 1851) (Orthoptera,Ensifera, Gryllacridoidea,Stenopelmatidae)

Summary This study of the ultrastructure of the auditory sensilla of the New Zealand weta, Hemideina crassidens, is the first such study on a member of the orthopteran Superfamily Gryllacridoidea. Ultrastructure of the auditory sensilla is similar in all of the tibial mechanosensory organs, here called subgenual organ, intermediate organ and crista acoustica by analogy with comparable structures in Tettigoniidae.Distal to each sensory soma is a dendrite containing multiple ciliary rootlets that fuse into a single ciliary root. This splits into nine root processes that pass around the outside of the proximal basal body and then rejoin at the level of the distal basal body, distal to which the dendrite has a modified ciliary structure with a circlet of nine peripheral paired tubes and rods as it passes through the proximal extracellular space. It is then enclosed by a zone of scolopale cell cytoplasm before expanding into a dilatation within the distal extracellular space. In some sensilla this space is partially occluded by electron dense material which is part of the scolopale cell. Distal to the dilatation the cilium shrinks and ends surrounded by the scolopale cap.Accessory cells consist of glia enwrapping the sensory neuron in the region of its soma, the scolopale cell surrounding the ciliary portion of the dendrite, and the attachment cell surrounding the scolopale cell and scolopale cap and connected to them by desmosomes. The attachment cells are filled with microtubules in differing densities and orientations. Lamellae are present in the acellular matrix surrounding the attachment cells. Banded fibres, presumably of collagen, are also present in the matrix.     

Johnston's organ in Neodiprion sertifer (Insecta: Hymenoptera)

The fine structure of Johnston's organ in the pine sawfly, Neodiprion sertifer, was studied by electron microscopy to determine if there exists a dimorphism in this organ corresponding to the sexual dimorphism in antennal shape and surface area. The organ is made up of scolopidia that are ultrastructurally similar to those of other insects. The scolopidia, identical in both sexes, comprise three sensory cells bearing two types of sensory processes: Two are shorter and smaller in diameter than the third, which extends into the cuticle of the membrane connecting pedicel and flagellum and terminates at an epicuticular invagination. The dendrites and sensory processes are surrounded by two types of enveloping (glial) cells-a scolopale cell and an attachment cell. Other enveloping cells occur at different levels of the scolopidium. Sexual dimorphism is evident only in the numbers of scolopidial groups: Males have more groups with fewer scolopidia, but both sexes possess about the same total number of scolopidia.     

东亚飞蝗Locusta migratoria manilensis（Mey．）膝下器中具橛感器的附属细胞和附属结构的超微结构

东亚飞蝗膝下器的具橛感器主要由三类细胞组成．即：感觉细胞、感橛细胞和冠细胞。感觉细胞为具橛感器的主要结构和功能细胞,其超微结构已在其他的文章中描述。感橛细胞是具橛感器的主要支持细胞,从近端到远端依次与神经胶质细胞、感觉细胞的远端树突部分和感觉纤毛部以及顶端细胞外结构——冠、冠细胞直接接触．感橛细胞内最明显的结构为感概,另外,感橛细胞质被高度“空化”。冠细胞紧密包围着感橛细胞和冠,冠细胞中含有大量的纵行微管．并将整个具橛感器连接到体壁上。     

The metathoracic wing-hinge chordotonal organ of an atympanate moth,Actias luna (Lepidoptera,Saturniidae): a light- and electron-microscopic study

Summary The structure of a simple chordotonal organ, the presumed homologue of the noctuoid moth tympanal organ, is described in the atympanate moth, Actias luna. The organ consists of a proximal scolopidial region and a distal strand, which attaches peripherally to the membranous cuticle ventral to the hindwing alula. The strand is composed of elongate, microtubule-rich cells encased in an extracellular connective tissue sheath. The scolopidial region houses three mononematic, monodynal scolopidia, each comprised of a sensory cell, scolopale cell, and attachment cell. The dendritic apex is octagonally shaped in transverse section, its inner membrane lined by a laminated structure reminiscent of the noctuoid tympanal organ collar. A 9+0-type cilium emerges from the dendritic apex, passes through both the scolopale lumen and cap, and terminates in an extracellular space distal to the latter. Proximal extensions of the attachment cell and distal prolongations of the scolopale cell surrounding the cap are joined by an elaborate desmosome, with which is associated an extensive electron-dense fibrillar plaque. Within the scolopale cell, this plaque constitutes the scolopale rod material. The data are discussed in terms of both the organ's potential function, and its significance as the evolutionary proto-type of the noctuoid moth ear.     

Structure of the tarso-pretarsal chordotonal organ in the imago of Tineola bisselliella Humm. (Lepidoptera : Tineidae)

The tarso-pretarsal chordotonal organ in the imago of Tineola bisselliella (Lepidoptera .: Tineidae) includes 2 groups of scolopidia. (1) A basal group composed of 2 scolopidia, each with one neuron and one scolopidium with 3 neurons, whose dendrites present a typical structure of cilium; the dendrite becomes dense apically; it is a common characteristic for all the mechanoreceptive dendrites. (2) An apical scolopidium with 3 neurons, whose dendrites have the same size and are covered with a conical cap.The combination of single and triple dendrites is unusual in the limb chordotonal organs. The 2 groups of scolopidia are not in contact. The importance of the support structures and fixation structures is discussed. In the ciliary root region, peculiar desmosomes occur between the dendrite and the scolopale cell. For the apical scolopidium, one attachment cell is seen distally and it appears in close association with the articular membrane.     

Functional morphology of the subgenual organ of the carpenter ant

Using light microscopy, confocal microscopy, electron microscopy and histochemistry, the subgenual organ (SGO) of an ant, Camponutas ligniperda, is investigated. Sensory units and attachment cells together enclose a large extracellular cavity, which is filled by acid mucopolysaccharides, as revealed by staining with ruthenium red. Due to this cavity, the whole SGO has the shape of a deformed sphere and the scolopidia exhibit a distribution of angles between 0 degrees and 60 degrees with the tibial long axis (as is shown by phalloidin-rhodamin staining of the actin filaments of the scolopale, viewed in situ by laser scanning confocal microscopy). The subgenual organ is innervated by a branch of the tibial nerve, which splits within or shortly distal to the femur-tibia joint. The other features of the SGO of Camponotus ligniperda are similar as in other insects: the SGO of Camponotus ligniperda contains about 35 scolopidial sensilla; it is fixed to the subgenual nerve on its proximal end, by its attachment cells to the opposite part of the cuticle; the fixation by the attachment cells is accomplished by a vast quantity of cytoplasmic microtubules; the construction of the sensory units is the same as in other mononematic scolopidial organs. The role of the extracellular lumen inside the organ and the special shape of the SGO of Camponotus ligniperda in mechanical transmission is discussed.     

Cytoskeletal elements in arthropod sensilla and mammalian photoreceptors.

Ciliary receptor cells, typified by cilia or modified cilia, are very common in the animal kingdom. In addition to the cytoskeleton of their ciliary processes these receptors possess other specific prominent cytoskeletal elements. Two representative systems are presented: i) scolopidia, mechanosensitive sensilla of various arthropod species; and ii) photoreceptor cells of the retina of the bovine eye. Two cytoskeletal structures are characteristic for arthropod scolopidia: a scolopale typifies the innermost auxiliary cell, and long ciliary rootlets are extending well into the sensory cells. The latter element is also characteristic for the inner segment of the photoreceptor cells in bovine. The scolopale of scolopidia is mainly composed of actin filaments. In the absence of myosin, the uniform polarity of the actin filaments and their association with tropomyosin all indicate a stabilizing role of the filament bundles within the scolopale. This function and a certain elasticity of actin filament bundles may be important during stimulation of the sensilla. The ciliary rootlets of both systems originate at the basal bodies at the ciliary base of the sensory cells and project proximally. These rootlets are composed of longitudinally oriented, fine filaments forming a characteristic regular cross-striation. An alpha-actinin immunoreactivity was detected within the ciliary rootlets of scolopidia. In addition, antibodies to centrin react with the rootlets of both types of receptors. Since centrin is largely responsible for the contraction of the flagellar rootlets in green algae, contraction may also occur in the ciliary rootlets of insect sensilla and vertebrate photoreceptors. In both systems, contraction or relaxation of the ciliary rootlets could serve in sensory transduction or adaptation.     

Actin filaments: the main components of the scolopale in insect sensilla

Summary Two types of insect sensilla, mechanosensitive scolopidia and thermo-/hygrosensitive poreless sensilla contain a scolopale, which consists of numerous microtubules embedded in bundles of filaments (7–10 nm in diameter). The bundles are readily seen in the electron microscope in cryofixed (high-pressure freezing and rapid injection) and substituted samples. The filaments can be identified as actin filaments by using fluorescent phalloidins. Both electron microscopy and Triton-extraction exeriments reveal mechanical linkage between the main components in both types of sensilla. Since myosin appears to be absent in the scolopale, the actin filaments are unlikely to be involved in any contraction mechanism; these filaments more probably provide mechanical stability. The functional properties of the scolopale are discussed.     

Structure of the abdominal receptor responsive to internally applied pressure in the blood-feeding insect,Rhodnius prolixus

Summary The sensory receptor responsive to pressure applied internally to the ventral abdominal body wall of the blood-feeding insects, Rhodnius prolixus, is a single sense cell containing, at its distal end, a cilium enclosed within a scolopale, a densely staining structure characteristic of insect scolopidial sensilla. A small spherical structure lies within a dilation near the midregion of the cilium, and contains nine heavily staining bodies, the position of each corresponding to a pair of microtubules in the cilium. Proximal to the dilation, the microtubules are organized in a ring of nine pairs with one microtubule of each pair associated with dyneinlike arms. Dastal to the dilation a central pair of microtubules is present, but dyneinlike arms are absent. The scolopale cell, which gives risc to the scolopale, has cytoplasmic invaginations that form an elaborate array of extracellular compartments surrounding the body wall of the sense cell. These compartments may serve to dampen high frequency vibrations permitting the receptor to respond to pressure exerted by touch, an attribute in keeping with the receptor's proposed function of detecting abdominal distension related to the size and movement of the stomach.     

Fine structure of scolopidia in Johnston's organ of female Aedes aegypti compared with that of the male.

The Johnston's organ of the female mosquito, Aedes aegypti, has only three types of scolopidia: types A, B, and C. It lacks the type D scolopidium of the male's organ. The basic structure and the location of each type in the female are similar to the counterparts in the male's organ. A single scolopidium is composed of a scolopale cell, an envelope cell, a long cap, and a third sheath, in addition to the two electron-dense scolopales produced inside the cytoplasm of two satellite cells. Each scolopidium has either two (type A) or three (type B) sensory cells. A type C scolopidium, mononematic in contrast to the amphinematic types A and B scolopidia, has two sensory cells, a microtubular cap cell, two microtubular accessory cells, and a scolopale cell with an intracellular scolopale. Even though the female Johnston's organ has all the components of the male's organ except for the single type D scolopidium, the female's organ shows relatively poorer organization and development. The female has a smaller and thinner basal plate, shorter and thicker prongs, fewer type A sensory cells, and a shorter flagellar flange, in addition to the overall smaller size of the pedicel.The probable function of each scolopidial type is discussed, especially in connexion with the probable identification of a single auditory sensillum in the male.     

Mechanism for range fractionation in chordotonal organs of Locusta migratoria (L) and Valanga sp. (Orthoptera : Acrididae)

The femoral chordotonal organ (FCO) of Locusta migratoria and Valanga sp. (Orthoptera : Acrididae) is a leg stretch receptor containing scolopophorous sensory neurones embedded in a ligament, which emerges distally from the body of the organ and connects to a distal apodeme. The ligament is pulled when the tibia is flexed. Thus the FCO bridges the femur-tibia joint. The ligament is divided into separate strands, each of which is composed of several or more, long attachment cells. These cells link individual scolopidia to the apodeme. An additional unloading strand connects the body of the FCO to a static point on the femoral integument. Because the strands are inserted along the apodeme in a sequential array, and because the unloading strand holds all the tension on the FCO when the ligament is relaxed (tibia extended), a mechanism for gradual, sequential uptake of tension by the ligament strands exists when the ligament is pulled (tibia flexed). This leads to a range fractionation of stretch-sensitive neurone responses during tibial flexion, and of relaxation-sensitive neurone responses during tibial extension. Observations on the ultrastructural distribution of desmosomes suggest that groups of attachment cells may be functionally connected and may collectively transmit force to specific groups of neurones.     

Structure,development and death of sensory cells and neurons in the pupal labial palp of the butterflies Pieris rapae L. and Pieris brassicae L. (Insecta,Lepidoptera)

Summary The development of neurons possibly related to the outgrowth of axons from the labial palp-pit organ was studied in Pieris rapae. Serial sections of six successive stages between pupation and emergence of the imago were examined with the electron microscope. At pupation the palp contains an apical scolopidial organ (ASO) and cellular strands connected to it. The ASO consists of three type-1 scolopidia, which are characterized by the presence of a ciliary 9 × 2 + 0 pattern throughout the dendritic outer segment and a ciliary dilation beneath the cap. The scolopidia show two special features: (i) the dendritic outer segments reach beyond the cap, and (ii) an intricate junctional complex develops between the dendritic inner segments and the scolopale cells. The cellular strands comprise two types of cells: (1) bipolar cells regarded as neurons due to their cytological features, and (2) enveloping cells, which are wrapped around the bipolar cells. The strands degenerate about 10 h after pupation. The sensory cells of the ASO degenerate consecutively between 28 h and 130 h after pupation. However, their enveloping cells survive and endure in the imago, which emerges about 160 h after pupation. An ASO similarly lacking sensory cells was observed in imagines of Pieris brassicae. It is hypothesized that the ASO and the bipolar neurons of the strands play a role in pathfinding of the axons of the labial palp-pit organ.Supported by the Deutsche Forschungsgemeinschaft (SFB 4/G1)     

Das tympanalorgan von Gryllus bimaculatus Degeer (saltatoria,gryllidae)

Zusammenfassung Das Tympanalorgan von Gryllus bimaculatus Degeer liegt an der lateralen Wand der vorderen Trachee and schließt sich unmittelbar an das Subgenualorgan an. Es besteht aus 3 eng beieinanderliegenden Abschnitten: dem proximalen Absehnitt (10–12 Scolopidien), den Scolopidien des hinteren Tympanalnervs (10–12 Scolopidien) and einem distalen Absehnitt (35–40 Scolopidien).Ein Scolopidium des Tympanalorgans besteht aus folgenden Zellen: einer bipolaren Sinneszelle, die sich nach distal in einen Sinnesfortsatz mit einem Sinnescilium fortsetzt, einer oder zwei Gliazellen, einer proximalen Hüllzelle, der Stiftzelle (= 1. Hüllzelle), der Kappenzelle (= 2. Hüllzelle) und der akzessorischen Zelle (= 3. Hüllzelle). Das Sinnescilium ist mit einem langen, sich aufspaltenden Wurzelfaden im Sinnesfortsatz verankert. An der Cilienbasis befinden sich zwei Basalkörper. Die Spitze des Ciliums reicht in einen Stiftkopf, der wie bei alien hemimetabolen Insekten nicht massiv ist. Unterhalb des Stiftkopfes erweitert sich die Cilie zu einer Ciliendilatation, deren Zentrum elektronendichtes Material enthält. Die Cilie verläuft in einem extrazellulären Raum, der durch Stützstrukturen innerhalb der Stiftzelle, den Wandrippen, aufrecht gehalten wird. Das Organ hat an der lateralen Wand des Beines eine schmale Anheftungsstelle; die Verankerung in der Epidermis erfolgt über die akzessorischen Zellen.

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The tyrnpanic organ of Gryllus bimaculatus Degeer (saltatoria, gryllidae)

Summary The tympanic organ of Gryllus bimaculatus Degeer is situated at the lateral wall of the anterior trachea just distal to the subgenual organ. It consists of three groups of sensilla lying quite close together: the proximal part (10–12 scolopidia), the scolopidia of the posterior tympanic nerve (10–12 scolopidia), and a distal part (35–40 scolopidia).Each scolopophorous sensillum of the tympanic organ is composed of the following distinct cells: the bipolar sense cell, which narrows to form the dendrite with the cilium, one or two glial cells, the proximal enveloping cell, the scolopale cell (= 1st sheath cell), the cap cell (= 2nd sheath cell), and the accessory cell (= 3rd sheath cell). The cilium is anchored within the dendrite with a long root, which divides into numerous rootlets. There are two basal bodies at the base of the cilium. The tip of the cilium projects into the cap, which, as in all hemimetabol insects, is not solid. Proximal to the cap the cilium widens into a dilatation containing electron-dense material in the centre. The cilium passes through an extracellular space, which is maintained by supporting structures, the rods, lying in the scolopale cell. The organ is attached to the epidermis of the wall of the leg by means of the accessory cells.

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Abkürzungen A Anheftungsstelle - äK äu\ere Kante der kleinen Trachee - akZ akzessorische Zelle - Ax Axon - Bk Blutkanal - Bz Blutzelle Das Tympanalorgan von Gryllus bimaculatus Deg Cd Ciliendilatation - Cu Cuticula - D Desmosom - dBa distaler Basalkörper - De Dendritenerweiterung - Dm Deckmembran - Ep Epedermis - ER endoplasmatisches Reticulum - ETk Epithel des Trachealkörperehens - Ex Extrazellularraum - F Fettgewebe - Fc Femur - Fi Fibrillen - fiF fingerförmige Fortsätze - G Gliazelle - Go Golgi-Komplex - Hd Hemidesmosom - hSn hinterer des Subgenualnervs - hT hinteres Tympanum - hTl hintere Tympanalleiste - hTr hintere Trachee - iN integumentaler Nerv - K Kappenzelle - M Mündung der klemen Trachee - Mi Mitochondrium - Mk Muskelkanal - Mt Mikrotubulus - Mu Muskel - N Nucleus - Nt Neurotubulus - Pi Pigment - pBa proximaler Basalkörper - pHz proximale Hüllzelle - prA proximaler Abschnitt - S Suspensorium - Sc Sinnescilium - Se Sehne - Sf Sinnesfortsatz - Si Stift - Sk Stiftkopf - Sn Subgenualnerv - So Subgenualorgan - Stz Stiftzelle - Sz Sinneszelle - Tan Tarsalnerv - Tf Tonofibrille - Ti Tibia - Tin Tibialnerv - Tk Trachealkörperchen - Tn Tympanalnerv - To Tympanalorgan - Tsn Subgenualast des Tympanalnervs - V Vakuole - vSn vorderer - Ast des Subgenualnervs - vT vorderes Tympanum - vTl vordere Tympanalleiste - vTr vordere Trachee - W Wurzelfaden - Wr Wandrippe - Wu Wulst Dissertation im Fachbereich Biologie der Universität Mainz.Herrn Professor Dr. H. Risler bin ich für die Themenstellung und für die gewährte Unterstützung zu Dank verpflichtet. Herra Professor Dr. K. Schmidt danke ich für die Einführung in die elektronenmikroskopische Technik und für wertvolle Anregungen und Hinweise.     

Ultrastructure des trichobothries de l'antenne de Campodea kervillei denis et Plusiocampa cognata conde (Apterygota : Diplura : Campodeidae)

Trichobothria are present on the 3rd to 6th antennal segments in Campodea kervillei Denis and Plusiocampa cognata Condé (Apterygota : Diplura : Campodeidae). Each is composed of one closed cuticular pit with a long, thin hair, arising from the bottom. Under the pit, lies a globular structure surrounded by a fibrillar substance. The sensorial axis is composed of 4 neurons, each giving a cilium. The largest shows a tubular body and reaches the hair base. Three envelope cells wrap the sensory axis; the inner exhibits small longitudinal rods of microtubules embedded in a dense substance, similar to a scolopale.     

Electron microscope observations on the submicroscopic organization of the retinal rods

The submicroscopic organization of the retinal rods of the rabbit has been studied with high resolution electron microscopy in thin longitudinal and cross-sections. The outer rod segment consists of a stack of flattened sacs or cisternae each of them limited by a thin homogeneous membrane of about 30 A. The membrane of the rod sacs is attached to the surface membrane and is also in continuity with short tubular stalks of about 100 to 150 A which apparently end in relation with the connecting cilium. The bundle of filaments that constitute the connection between the outer and the inner segments is described under the name of connecting cilium. This fibrous component has a structure that is very similar to that of the cilium. It shows 9 pairs of peripheral filaments of about 160 A in diameter, a matrix material, and a surface membrane. Very infrequently two central single filaments are observed. The connecting cilium has a typical basal body in the inner segment; its distal end penetrates the outer segment, where it establishes some structural relation to the rod sacs. The relationships and submicroscopic organization of the connecting cilium were studied in longitudinal and in cross-sections passing at different levels of the rod segments. The inner rod segment shows two distinct regions: a distal and a proximal one. The distal region, corresponding to the ellipsoid of classical histology is mainly composed of longitudinally packed mitochondria. It also contains the basal body of the cilium, vacuoles of the endoplasmic reticulum, dense particles, and intervening matrix with very fine filaments. In the proximal region of the inner segment the mitochondria are lacking and within the matrix it is possible to recognize elements of the Golgi complex, vacuoles of the endoplasmic reticulum, dense particles and numerous neuroprotofibrils of 160 to 200 A in diameter which collect and form a definite bundle at the exit of the rod fiber. The interpretation of the connecting fibers as a portion of a cilium and of the outer segment as a differentiation of the distal part of a primitive cilium are discussed. The importance of the continuity of the surface membranes of the outer segment, connecting cilium, and inner segment is emphasized and its possible physiological role is discussed.     

Structure of atympanate tibial organs in legs of the cave-living ensifera,Troglophilus neglectus (Gryllacridoidea,Raphidophoridae)

Troglophilus neglectus (Gryllacridoidea, Raphidophoridae) is a nocturnal Ensifera which can be found in caves of Slovenia. The anatomy of the tibial organs in the fore-, mid-, and hindlegs, as well as the external morphology of the proximal fore-tibia and the prothoracic tracheal system, is described comparatively. In the prothorax and in the forelegs, no sound-conducting structures such as an acoustic trachea, enlarged spiracles, or tympana are developed. A group of 8–10 campaniform sensillae is located in the dorsal cuticle of the proximal tibia. In each leg, the tibial organ complex is built up by two scolopale organs, the subgenual organ and the intermediate organ; the structure and the number of scolopidia is similar in each leg. No structure resembling the crista acoustica is found. The subgenual organ contains around 30 scolopidia; the intermediate organ is subdivided into a proximal part containing 8-9 scolopidia and a distal part with 5–6 scolopidia. The two groups of scolopidia are not directly connected to the tracheal system. The tibial organs in the forelegs are insensitive to airborne sound, and they appear to be more primitive compared to those found in members of the Tettigoniidae and the Gwllidae. The results indicate that the complex tibial organs in all legs of T. neglectus are primarily vibrosensitive. © 1995 Wiley-Liss, Inc.     

Fine structure of the statocyst sensilla of the mysid shrimp Neomysis integer (Leach, 1814) (Crustacea,Mysidacea)

The fine structure of the statocyst sensilla of Neomysis integer was investigated. The statocyst contains about 35 sensilla, which are composed of two bipolar sensory cells, nine enveloping cells, and a seta. The sensory cells consist of an axon, a perikaryon, and a dendrite. The dendrite contains a proximal segment with a ciliary rootlet and at least one basal body, and a distal segment with a ciliary axoneme (9 × 2 + 0) at its base. The distal segment extends along the peripheral wall of the seta and is in close contact with the wall of the hair shaft. The enveloping cells surround the proximal and distal segments of the dendrite. The innermost enveloping cell contains a scolopale rod. It surrounds the receptor lymph cavity and secretes flocculent material into this cavity. From the tip of the cell a dendritic sheath, which encloses the distal segment of the dendrite, emerges. A peculiar feature of the second enveloping cell is the presence of a scolopale-like rod, which is more slender and less pronounced than in the first enveloping cell. The seta consists of three parts: a socket, a tubular midpart, and a gutter-like apical part, the tip of which penetrates into the statolith. The seta shows over its full length a bilaterally symmetrical axis that is coplanar with the plane in which the seta is bent toward the statolith. The structure of the seta and the position of the distal segments provide morphological evidence for directional sensitivity of the sensilla and for the magnitude of shear on the setal wall being an adequate stimulus.     

Are the funnel-canal organs the ‘campaniform sensilla’ of the shore crab,Carcinus maenas (Decapoda,Crustacea)?

Summary 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 m. 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 m 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 mechano-sensitive 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.     

Embryogenesis of the connective chordotonal organ in the pedicel of the American cockroach: Cell lineage and morphological differentiation

Summary The ontogenesis of single scolopidia of the chordotonal organ of the American cockroach, Periplaneta americana, takes about 4 days. At 23% embryogenesis (100% = 30 d) the first anlagen of scolopidia were identified within the epithelium by staining with anti-horseradish peroxidase. Reconstruction of the cell lineage of the scolopidial cells was facilitated by two facts: (i) the arrangement of the cells throughout ontogenesis follows a strict pattern, and (ii) daughter cells are recognizable for several hours after mitosis by the cytoplasmic bridge and midbody joining them. When they separate, the midbody undergoes lysosomal degeneration in one of these cells. The earliest recognizable stage is a pair of cells, one of which (cell 1) encloses the other (cell 2) apically. The enclosing cell becomes the accessory cell. Cell 2 divides, yielding the mother cell (cell 3) of two sensory cells which degenerate later, and cell 2. Cell 2 gives rise to the attachment cell and to cell 2, which in turn produces the scolopale cell and the mother cell (cell 2 2) of a second pair of sensory cells; the latter are the definitive sensory cells. The end result is the total of 5 cells characteristic of the adult scolopidium. Secretion of the scolopale and cap together with the migration of the sensory cell perikarya into the antennal lumen complete development.