The segmentation of the gnathobdellid leeches with special reference to the Indian leech Hirudinaria and medicinal leech Hirudo

Large number of annuli in Hirudinea are not true segments, and in the absence of spacious bodycavity and septa in adult no decision was taken regarding limit of a somite, until Gratiolet 1862 recognised a segment by colour marking, repetition of nephridial openings, and especially by the presence of segmental receptors, distinguishing first annulus of a segment. Whitman 1884 gave precision to these determinations and analyzed morphology of leeches to logical completeness. He recognised that though Hirudinaria and Hirudo have 102 body annuli and posterior sucker, true segments are only 26 plus 7. Castle ('00) and Moore ('00) proposed a new scheme of segmentation, with segmental receptor bearing annulus, as central annulus of a complete somite, with nerve ganglion, like that of other annelids, in center of a segment. They orientated everything roundabout the ganglion without noticing distorted fate of organ system. In this paper both the views are compared. Morphological and embryological studies reveal that the annulus bearing the segmental receptors in uniformly first annulus of all segments, including incomplete segments at the two extremities, with nerve ganglion in first annulus of the segment. Clitellum occupies three natural segments, IX, X, XI; crop caeca, nephridia, testis sacs, haemocoelomic channels and “rhomboidal figures” formed by ventrolaterals, all make a complete unit, well integrated in such segment. Conclusive evidence comes from the presence of septa at the level of each nerve ganglion in embryos of Hirudinaria. These observations corroborate Gratiolet and Whitman's view.     

External sensilla of the locust abdomen provide the central nervous system with an interganglionic network

External mechanoreceptors and contact chemoreceptors on the cuticle of the sixth abdominal segment of locusts have divergent primary projections of their sensory neurons that form arbours in the segmental and anterior abdominal ganglia. Homologous interganglionic projections from adjacent segments converge in the neuropile of each abdominal ganglion. Of the contributing types of sensilla, three were previously unknown for locust pregenital segments: tactile mechanosensory hairs with dual innervation, external proprioceptors of the hairplate type covered by intersegmental membranes and single campaniform sensilla that monitor cuticular strain in sternites and tergites. In general, interdependence of motor coordination in the abdominal segments is based on a neural network that relies heavily on intersegmental primary afferents that cooperate to identify the location, parameters and strength of external stimuli.     

Ultrastructure of the water-movement-sensitive sensilla in the medicinal leech

Behavioral and physiological experiments have shown that medicinal leeches are able to detect low amplitude surface waves, and further, that the transduction of this stimulus modality occurs primarily, if not exclusively, at the annular sensilla (Young, Dedwylder, and Friesen, 1981; Friesen, 1981). Here we examine the morphology of these specialized sensory structures using light, scanning electron, and transmission electron microscopes. We found that three types of ciliated sensory cells occur at the sensilla: (1) a uniciliate cell, with an axial cilium that projects at least 12 μm beyond the cuticle; (2) a multiciliate cell with from two to four grouped cilia that extend 1–3 μm beyond the cuticle; and (3) a second multiciliate cell, whose cilia project parallel to the body surface but remain within the cuticle. The cilia of all three cell types arise from the cuplike depressions which form the apices of slender, elongated cells (approximately 2 μm diameter × 50 μm length). A complexly interconnected ring of microvilli surrounds the cilium of the uniciliate cells. The morphology of the uniciliate cells closely resembles the structure of vibration-sensitive sensory neurons found in other species. We propose, based on previous results and our new findings, that the uniciliate receptor cells are the sensillar movement receptors which mediate leech sensitivity to water movements.     

Changes in distribution and abundance of antennal sensilla during growth of Locusta migratoria L. (Orthoptera : Acrididae)

The antenna of Locusta migratoria (Orthoptera : Acrididae) increases in length by the production of new annuli proximally and by elongation of existing annuli. The most distal annuli are fully differentiated at the time of hatching and no new olfactory sensilla are added to them at subsequent molts. More proximally, the differentiation of trichoid contact chemoreceptors precedes the development of olfactory sensilla. Sensillum differentiation proceeds from distal to proximal along the antenna and more distal annuli attain full development at each molt. The biggest increase in numbers of olfactory sensilla occurs at the final molt. On any one annulus, most olfactory sensilla are restricted to sensory fields on the anterior and posterior faces. Their spacing within these fields is consistent with the existence of separate but interacting chaetogens regulating the differentiation of basiconic and coeloconic sensilla.     

The Anatomy of the Tarsi of Schistocerca gregaria Forskål

Summary The tarsus of S. gregaria is divided into three units (here called segments) and an arolium set between a pair of claws. The first segment bears three pairs of pulvilli in the fore and middle legs, and one pair and two single pulvilli in the hind legs. Segment two bears a pair of pulvilli, segment three one long pulvillus and the arolium a similar pad on the undersurface. The outer layers of the arolium pad differ from those of the pulvilli in possibly lacking an epicuticle and in having a layer of cuticle which, unlike the corresponding layer in the pulvilli, does not stain with protein stains. The claws and dorsal surfaces bear trichoid sensilla, basiconic sensilla and campaniform sensilla. Smaller basiconic sensilla and canal sensilla occur on the proximal part of the pulvilli, and basiconic sensilla on the arolium undersurface. Internally the cuticle is modified in the arolium and pulvilli so that rods of probably chitin and resilin are formed. This would impart flexibility to the undersurfaces whilst retaining some degree of rigidity which might prevent damage to the small and delicate sense organs on the pulvilli. The tip of the arolium is specialised for adhesion, and there are two large neurones internally which could conceivably monitor attachment or detachment of the tip. There are chordotonal organs in segment three, and several other large neurones throughout the tarsus, some of which are associated with the slings of tissue holding the apodeme in a ventral position. Gland cells occurring in the dorsal epidermis of the adult mature male are also briefly described.     

Sensory Organs in Ips typographus (Insecta: Coleoptera) Fine structure of the sensilla of the maxillary and labial palps*

The labial and maxillary palps of the bark beetle, Ips typographus, possess a diversified array of sensilla. There are four types of sensilla possessing a single tubular body indicating a mechanoreceptive function. The variation of the associated cuticular structures of these sensillar types ranges from long bristles to cavities within the cuticle. Terminal pore sensilla with a supposed mechanosensory/gustatory function and single-walled presumably chemoreceptive sensilla are found on the apical part of the terminal palp segments. A poreless sensillar type is found on the lateral side of the terminal segment of the maxillary palp. The functional capabilities of this sensillar type are presently unknown.     

Sensilla on the mouthparts and antennae of the elephant louse,Haematomyzus elephantis piaget (Phthiraptera: Haematomyzidae)

The labial palpus of the elephant louse Haematomyzus elephantis has six sensilla that represent three different types: trichoid, basiconic, and styloconic. Two rows of basiconic sensilla are situated on the dorsal and ventral surfaces of the rostrum, and each row consists of three sensilla. Male and female antennae have 15–17 trichoid sensilla situated on the scape, pedicel, and three antennal annuli. Both sexes have two sensilla basiconica on the dorsal surface of the pedicel near the junction of the scape and pedicel. Two coeloconic (tuft) sensilla are situated on the antennae of both sexes, one sensillum on each of the last two annuli. There are three plate organs, two on the last annulus and one on the penultimate annulus of the male and female antennae. Sexual dimorphism is exhibited in the male and female antennae, in that the male has about twice as many sensilla basiconica on the apex of the last annulus as does the female. The total number of sensilla basiconica on the apex of the male antennae is at least two times the number that is known to be present in any other species of lice. © 1992 Wiley-Liss, Inc.     

大豆蚜触角嗅觉感器结构及其功能

采用扫描电镜观察大豆蚜Aphis giycines各型触角上嗅觉感器的细微结构,结合触角电位记录,发现大豆蚜有翅孤雌生殖蚜对萜烯衍生物的感受部位在第6节原生感器上,而萜烯烃类则在第5节原生感器上,两原生感器都对绿叶气味和芳香类起嗅觉反应。末端2节上还有其它化学感器对植物气味起反应。因此,各型对植物气味的感觉部位在末端2节上。各型对报警信息素的作用部位主要在第6节原生感器上,无翅型第5节原生感器和有翅型第3节次生感器也有一定的感觉能力。     

Structure and development of antennae in a moth,Manduca sexta

The antenna of the moth, Manduca sexta, comprises two small basal segments and a long (2 cm) flagellum, which is divided into nearly 80 annuli. The annuli bear cuticular scales and small sensory organs, sensilla. A trachea, a blood vessel, and two nerve trunks run through the lumen of the antenna and into the head. Sensilla are arranged in an orderly pattern that is repeated on each flagellar annulus. Each flagellum bears about 10⁵ sensilla, which contain about 2.5 × 10⁵ primary sensory neurons. Clumps of undifferentiated cells (imaginal disks), present in the larva, form pupal antennae during the larval-pupal molt. During the subsequent metamorphic development of the adult, cell divisions, changes in cell shape, and cellular differentiation transform pupal into adult antennae. Sensilla and scales arise and differentiate in the antenna during metamorphosis; regions in which sensilla and scales will arise can be recognized before overt differentiation occurs. All of the flagellar annuli develop synchronously. The dense innervation and neuronal simplicity of antennal flagella, as well as their synchronous development at a late and accessible stage in the animal's life cycle, suit them for studies of neuronal differentiation.     

Morphogenesis of the antenna of the male silkmoth. Antheraea polyphemus, III. Development of olfactory sensilla and the properties of hair-forming cells

During adult development of the male silkmoth Antheraea polyphemus, the anlagen of olfactory sensilla arise within the first 2 days post-apolysis in the antennal epidermis (stage 1-3). Approximately on the second day, the primary dendrites as well as the axons grow out from the sensory neurons (stage 4). The trichogen cells start to grow apical processes approximately on the third day, and these hair-forming 'sprouts' reach their definite length around the ninth day (stages 5-6). Then the secretion of cuticle begins, the cuticulin layer having formed on day 10 (stage 7a). The primary dendrites are shed, the inner dendritic segments as well as the thecogen cells retract from the prospective hair bases, and the inner tormogen cells degenerate around days 10/11 (stage 7b). The hair shafts of the basiconic sensilla are completed around days 12/13 (stage 7c), and those of the trichoid sensilla around days 14/15 (stage 7d). The trichogen sprouts retract from the hairs after having finished cuticle formation, and the outer dendritic segments grow out into the hairs: in the basiconic sensilla directly through, and in the trichoid sensilla alongside, the sprouts. The trichogen sprouts contain numerous parallel-running microtubules. Besides their cytoskeletal function, these are most probably involved in the transport of membrane vesicles. During the phase of cuticle deposition, large numbers of vesicles are transported anterogradely from the cell bodies into the sprouts, where they fuse with the apical cell membrane and release their electron-dense contents (most probably cuticle precursors) to the outside. As the cuticle grows in thickness, the surface area of the sprouts is reduced by endocytosis of coated vesicles. When finally the sprouts retract from the completed hairs, the number of endocytotic vesicles is further increased and numerous membrane cisterns seem to be transported retrogradely along the microtubules to the cell bodies. Here the membrane material will most probably be used again in the formation of the sensillum lymph cavities. Thus, the trichogen cells are characterized by an intensive membrane recycling. The sensillum lymph cavities develop between days 16-20 (stage 8), mainly via apical invaginations of the trichogen cells. The imago emerges on day 21.     

Morphology and distribution of antennal sensilla of the tarnished plant bug,Lygus lineolaris (Palisot de beauvois) (Hemiptera: Miridae)

Sensilla on the antennae of adult and last-instar nymphs of the tarnished plant bug, Lygus lineolaris (Hemiptera: Miridae), were examined with light, scanning and transmission electron microscopy. Six different types were identified in adult females and males and 5 types in last-instar nymphs: types 1 and 4 are sensilla trichodea, 2 and 3 are sensilla chaetica, and 5 and 6 are sensilla basiconica. Type 1 are located at distal region of terminal segment and type 2 are located at distal regions of proximal 3 segments in both adults and nymphs. Type 3 is present on all segments, more numerous on scape and pedicel and less abundant on distal third and fourth segments in both adult and nymphal stages. Types 4 and 6 are absent on the scape and present on the distal 3 antennal segments in adults, but they are present only on the distal-most antennal segment in nymphs. Type 5 sensilla are present only on second antennal segments in adults and are absent in nymphs. Sexual dimorphism is observed in total numbers: there are significantly more type(s) 3, 4, 5 and 6 sensilla in adult males than adult females. Types 1, 4 and 5 are multiporous with thin cuticle, branched dendrites and pore tubules which suggests an olfactory function. These sensilla have 3, 3 and 2 neurons, respectively. The type 6 sensillum has an apical pore and pores in the cuticular wall, and is innervated by 5 nerve cells with unbranched dendrites. Sensillar types 2 and 3 have thick cuticle, a single apical pore and nerve cells with unbranched dendrites. Type 2 has 1 neuron and type 3 has 2 chambers and 2 nerve cells.     

The cercal receptor system of the praying mantid,Archimantis brunneriana Sauss.

Summary The cerci of the praying mantid, Archimantis brunneriana Sauss., are paired segmented sensory organs located at the tip of the abdomen. Basally the cercal segments are slightly flattened dorso-ventrally and are fused to such a degree that it is difficult to distinguish them. Distally the segments become progressively more flattened laterally and their boundaries become more obvious.Two types of sensilla are present on the cerci, trichoid sensilla and filiform sensilla. Trichoid hairs are longest on the medial side of the cerci and toward the cercal base. On the proximal cercal segments they are grouped toward the middle of each segment while they are more uniformly distributed on the distal segments. Filiform sensilla are found at the distal end of each segment except the last and are most abundant on the middle segments of the cercus. Both the number of cercal segments and the number of sensilla are variable. Trichoid hairs are highly variable in appearance from short and stout to long and thin. They arise from a raised base, have a fluted shaft, and some have a pore at the tip. They are innervated by from one to five dendrites, one of which is always considerably larger than the others. Some of the dendrites continue out into the shaft of the hair.Filiform hairs have fluted shafts and are mounted in a flexible membrane within a cuticular ring in a depression. They are innervated by a single large sensory neuron, the dendrite of which passes across a flattened area on the inner wall of the lumen of the hair. The dendritic sheath forms the lining of the ecdysial canal and is therefore firmly attached to the hair. The dendrite is attached to the sheath by desmosomes distally and is penetrated by projections of the sheath more proximally. A fibrous cap surrounds the dendrite and may hold it in place relative to the hair.The cercal receptor system of Archimantis is compared to those of cockroaches and crickets.     

Fine structure of antennal mechanosensilla of adult Rhodnius prolixus stål (Hemiptera: Reduviidae)

Each antenna of both sexes of adult Rhodnius prolixus has approximately 570 mechanosensitive neurons that innervate five morphologic types of cuticular mechanosensilla: campaniform sensilla, tapered hairs, trichobothria, and type I and type II bristle sensilla. Each campaniform sensillum and tapered hair is presumably innervated by one mechanosensitive bipolar neuron and probably functions in proprioception. The campaniform sensilla being located at the base of the scape could monitor the position of the antenna. Tapered hairs are found at the distal margin of flagellar segment I and projecting laterally from the bases of the pedicel and scape. They probably provide information about the relative positions of the antennal segments. Seven trichobothrium are located on the pedicel and three on flagellar segment I. Each trichobothrium has a long filamentous hair inserted into the base of a socket that extends inwardly as a cuticular tube and is innervated by one bipolar neuron with a tublar body, a parallel arrangement of microtubules associated with electron-dense material. The trichobothria may respond to small variations in air currents. Type I bristles occur at the base of the antenna and are the most numerous type of mechanosensillum; an average of 452 occur on each antenna of females and 440 on males. The bristle is curved toward the antennal shaft and is serrated distally. Type II bristles are located distally and are the second most numerous type of mechanosensillum; an average of 88 were counted on each antenna of females and 94 on males. The type II bristle is straight with small, longitudinal, external grooves and projects laterally from the antennal shaft. Each type I and II bristle sensillum is innervated by a bipolar neuron whose dendrite is divided into an inner and outer segment. The outer segment is encased by a dendritic sheath which may be highly convoluted and distally contains a tubular body. Two sheath cells are associated with each sensillum. Both types of bristle sensilla have a tactile function. The tubular bodies of both types of bristle sensilla have a complex structure indicating that they are very sensitive. Variations in the amount and arrangement of the electron-dense material at the tip of the tubular bodies may reflect differences in viscoelastic properties that underlie functional characteristics.     

Molecular composition of the wall of insect olfactory sensilla-the chitin question

Identification of chitin in sensory hairs of olfactory sensilla of silkmoths was performed using two independent methods. Firstly, ultrathin sections were labelled with gold-conjugated wheat germ agglutinin and showed positive labelling in the cuticule of sensilla as well as in the antennal cuticle. Secondly, isolated sensory hairs and body scales were subjected to analytical pyrolysis in combination with gas chromatography and mass spectrometry. Chromatograms of both sensory hairs and scales, included several pyrolysis products, which unequivocally demonstrate the contribution of chitinous moieties to the chemical composition of both types of cuticle. This study supports the notion that even the very thin cuticle of olfactory sensilla is composed of both an epi- and a true exocuticle. The carbohydrate components of the latter cuticle most probably are responsible for the extremely high resilience and breaking limit of these delicate structures.     

Antennal sensilla ofNeomysis integer (leach)

Summary The most frequent type of the hair sensilla on the antennae ofNeomysis integer is investigated by electron microscopic methods. The cellular properties of the sensilla are compared with those of other arthropods in order to detect possible homologies.The hairs are innervated by 2, 3, 6, 8, 9, or 10 sensory cells. The dendrites show an inner and outer dendritic segment. Five or six enveloping cells belong to a sensillum. In intermoult stage, processes of all the enveloping cells except the innermost one extend into the hair shaft. The sensory hairs possess only a single liquor cavity, which morphologically is homologous to the inner lymph cavity of insect sensilla. Around the liquor cavity, a supporting structure is located which seems to be identical to the scolopale of chordotonal organs. The six-to tenfold-innervated hairs possess two groups of differently structured dendrites which are regularly arranged on opposite sides of the liquor cavity. The outer dendritic segments are enclosed in a dendritic sheath. It is secreted by the innermost enveloping cell (= dendritic sheath cell of insect sensilla). All the outer dendritic segments terminate in the distal region of the hair shaft which shows a pore at its tip. The possible function of the sensilla is discussed. The double and triple-innervated hairs are considered to be mechano-receptors, whereas the sensilla associated with six to ten sensory cells might be mechano-chemoreceptors.     

Head morphology of 1st and 5th instar nymphs of Triatoma circummaculata and Triatoma rubrovaria (Hemiptera,Reduviidae)

Morphological structures of the head of 1st and 5th instar nymphs of Triatoma circummaculata and Triatoma rubrovaria were revealed by analysis using scanning electron microscopy (SEM). Differences between 1st and 5th instar nymphs of these two species were observed in the postocular callosity, the number of ommatidia and tapered hair, the small segment between antennal segments, the rostrum third segment and slit lines. These slit lines were different only in the 5th instar. Similarities observed were the presence of tapered hairs in the joints, and the type of sensilla in the antennal segments. Only the 1st instar shows anteclypeus and gena sensilla. The antennal segments comprise the following types of sensilla: basiconica, bristles type I, bristles type II, bristles type III, campaniformia, coeloconica, chemosensilla, placodea, trichobothria and trichoidea. We describe here for the first time six (3+3) sensilla basiconica on the dorsal portion of the first segment of the rostrum.     

Fine structure and molting of aesthetasc sense organs on the antennules of the isopod,Asellus aquaticus (Crustacea)

In Asellus aquaticus certain distal antennular segments bear single sensilla referred to as aesthetascs. These show a proximal stem and a distal bulbous region. Depending on its position, each aesthetasc is innervated by either 50-60 or 70-80 bipolar sensory cells, the perikarya of which are situated within the pedunculus. Within the antennular segment the dendrites develop unbranched cilia (9 X 2 + 0 structure). The sensory cells are unusual in that mono- as well as biciliary dendrites are present within a single aesthetasc, the ratio of both types being correlated with the number of sensory cells. Cilia and receptor lymph cavity are enveloped by a set of 3-4 inner and 13-14 outer sheath cells, which terminate at the base of the sensillum, so that the delicate and poreless cuticle of the bulbous region encloses only outer segments within the receptor lymph fluid. A new molting type in arthropods is described in which the outer sheath cells alone build the new cuticle, whereas the inner sheath cells most probably have a protective function. A definition of aesthetascs is proposed based on fine-structural criteria. Functionally the sensilla are considered to be chemoreceptors. This assumption is confirmed by experiments with diluted vital dye as well as lanthanum showing that dissolved substances penetrate the poreless cuticle instantaneously.     

Sensory organs on the body parts of the bed-bug Cimex hemipterus fabricius (Hemiptera : Cimicidae) and the anatomy of its central nervous system

Anatomy of the sensory organs on the prominent body parts of the adult bed-bug Cimex hemipterus (Hemiptera: Cimicidae) and its central nervous system (CNS) was studied by light, transmission, or scanning electron microscopy. The distal tips of antenna and rostrum were found to have rich complements of sensilla. The antenna has both olfactory and gustatory sensilla. Olfactory sensilla project to the antennal lobe organized in the form of glomeruli, while the 2nd component, presumably from gustatory sensilla, projects to the suboesophageal ganglion. The ultrastructure of the sensory pegs on the rostrum of C. hemipterus does not resemble the chemosensilla of adult insects; rather they resemble the larval sensilla of Drosophila melanogaster in the maxillary organ. Earlier we believed this to be a gustatory organ. A few similar sensilla also occur on the antenna, indicating its multimodal role. Amongst the 3 types of sensory hairs located on legs, there are only a few gustatory hairs (7–10 hairs) on the tibia. The pointed and serrate mechanosensory hair types occur in abundance; the serrate type are prominently present on the lateral surface of the legs. On other parts of the body such as the thorax or abdomen, serrate hairs are most abundant. Both the distal segment of antenna and rostrum are invested by 2 nerves, where the axon counts of the 2 antennal nerves are 380 and 425, while each rostral nerve on average has 205 axons. Abundant clusters of microtubules were found in the brain, thoracio-abdominal ganglia, leg-nerves, and the space between muscles and cuticle. These conspicuous microtubule-clusters occur in interaxonal space, mainly glial cells, in the nervous system. In addition, the glial cells have osmiophilic junctions amongst themselves. A novel “hinge and joint” system, which controls the cross-section of the food canal and the salivary duct in an inversely related manner, was found in the rostrum of the bed-bug.     

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     

Distribution and fine structure of antennal olfactory sensilla in Japanese dung beetles,Geotrupes auratus Mtos. (Coleoptera : Geotrupidae) and Copris pecuarius Lew. (Coleoptera : Scarabaeidae)

The distribution and fine structure of olfactory sensilla on the antennal flagella of the Japanese dung beetles, Geotrupes auratus (Coleoptera : Geotrupidae) and Copris pecuarius (Coleoptera : Scarabaeidae) were studied by scanning and transmission electron microscopy. In both types of dung beetles, sensilla on the antennal segments were most abundant on the apical 3 lamellar segments, where sensilla basiconica were particularly concentrated. The sensilla were solely concentrated in the central part of the distal side of both the 9th and 10th segments in G. auratus and the 7th and 8th segments in C. pecuarius, respectively. The numbers of sensilla in these areas (channels) of the 9th and 10th segments in G. auratus were approximately 4,500 and 3,000, respectively. In C. pecuarius, there were about 1,900 sensilla on the 7th segment and l,700 sensilla on the 8th. The cuticles of the sensilla in both species were perforated by numerous elongate pores, with a pore density of about 45/ μm² in G. auratus and 30/ μm² in C. pecuarius. Each sensillum basiconicum in C. pecuarius was generally associated with 2 sensory neurons. The sensory cilia passed into the sensillum lumen and branched profusely, occupying most of its space. On the basis of the fine structure and dense location, these sensilla are considered to have an olfactory function for food detection.