Reconstruction and morphometry of silkmoth olfactory hairs: A comparative study of sensilla trichodea on the antennae of male Antheraea polyphemus and Antheraea pernyi (Insecta,Lepidoptera)

Summary Olfactory trichoid hairs on the antennae of male Antheraea silkmoths were reconstructed with respect to the following parameters: number, shape, course, and dimensions of outer dendritic segments as well as the numbers of their microtubules; inner and outer dimensions of the cuticular hair shafts; and number and distribution of pores and pore tubules in the hair walls. The smallest distances between dendritic membranes and inner hair surfaces were determined with respect to the possibility of pore tubule contacts. It was shown that most hairs contain one thick and one, or frequently two, thin dendrites. The number of microtubules in the dendrites is correlated with dendrite diameter, which decreases towards the hair tip. The dendrites form numerous swellings and constrictions: this beading occurs especially along the thin dendrites. The dendrites do not run straight, but rather follow a sinuous course in the hairs. The density of wall pores is lowest in the basal region of the hairs. Only in relatively few places do the dendritic membranes get near enough the hair walls to come into the probable range of the pore tubules. In the sensilla trichodea of A. polyphemus, the hairs as well as the dendrites have markedly smaller diameters than in A. pernyi.     

The Fine Structure of a Sensory Organ of a Cladocop Ostracode (Crustacea) Belonging to the Organ of Bellonci (Sensory Pore) Complex

Andersson, A. 1980. The fine structure of a sensory organ of a cladocop ostracode (Crustacea) belonging to the organ of Bellonci (sensory pore) complex. (Department of Zoology, University of Lund, Sweden.) — Acta zool. (Stockh.) 61(1): 51–58. The organ of Bellonci, a complex of cephalic receptors, has previously been reported from two ostracode groups. On morphologic grounds, a cephalic receptor of a third ostracode group (Cladocopa) is believed to be an organ of Bellonci. The organ is situated on the forehead above the first pair of antennae and consists of two feathered hairs. Two nerves, each formed by one dendrite, run from the protocerebrum into the hairs where they terminate with ramose cilia. The dendrites, as well as the cilia and ciliary branches, are enveloped by glial cells. Distally, these cells form cavities around the ciliary branches. The ciliated neuronal connection and the glial cavities, together with other morphologic characteristics of the organ, support a homologization with the organ of Bellonci of other myodocopid ostracodes.     

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.     

Interactions of pheromone with moth antennae: Adsorption,desorption and transport

Isolated antennae of the male moth Antheraea polyphemus adsorbed at least 32% of ³H-labelled pheromone molecules (E-6,Z-11 hexadecadienyl acetate) from an airstream passing the antenna. About 80% of the adsorbed molecules were caught by the long olfactory hairs (sensilla trichodea). The distal half of the hairs caught about twice as many molecules as the proximal half. About 40% of the molecules desorbed if the antennae were exposed to a clean airstream for 30 min. The adsorbed molecules were transported from the hairs towards the antennal branch. Transport due to diffusion would have a diffusion coefficient of 3 × 10^?7 cm²/s. Forty per cent of the total radioactivity per hair could be detected in receptor lymph extruded from the olfactory hairs, after an incubation time of 2 min. Dried antennae showed an increased desorption and an increased velocity of the transport along the hairs. One interpretation is that the molecules enter the receptor lymph of the intact antennae and diffuse more slowly than those on the cuticular surface. Fractional elution of fresh antennae revealed a diminishing elutability of pheromone from antennae in pentane (DEP-effect) and almost constant elutability in more polar solvents (chloroform-methanol toluene). The DEP-effect could be reversibly abolished by dehydration of the antennae. It could be shown that the DEP-effect occurs mainly on the antennal branch rather than on the hairs. Residual (uneluted) radioactivity builds up mainly on the branch.     

Fine structure of the tip of the labellar taste hair of the blow flies,Phormia regina (Mg.) and Calliphora vicina R.-D. (Diptera,Calliphoridae)

Summary The labellar taste hairs of the blow flies, Phormia regina and Calliphora vicina, have an opening mechanism at the tip which consists of two stump cuticular prongs and a funnel-like cuticular pouch. Opening and folding of these structures are regulated by the pressure within the dendrite-free lumen of the hair. The extrusion of viscous substance at the tip of the taste hair is possible through spongy cuticle and one pore in each prong; it seems likewise to depend on the pressure within the dendrite-free lumen and results in regional collapsing of this lumen. Described and discussed are: The cuticle and pores of the structures at the hair tip, pore filaments which extend from the dendrites, and the number and arrangement of the dendrites.This work was supported by a grant from the 7USDA, Entomology Research Division, Beltsville, Md., and the grant GB-13500 from the National Science Foundation.We thank Dr. J. F. Worley, USDA, Plant Science Research Division, Beltsville, Md., for his collaboration in fluorescence microscopy.     

External morphology of antennae and their sense organs in the roach Gromphadorhina brunneri (Blattoidea: Dictyoptera)

The antennae and their sense organs in nymphs and adult roaches of Gromphadorhina brunneri, were investigated and described. The number of segments and sensillae of the nymphal antennae depend on the developmental stage. Sexual dimorphism is pronounced. Males have longer antennae than females as well as an abundance of especially long sensory hairs (long wavy hairs), which are probably responsible for the perception of female sex pheromones. They also have more thin-walled sensory hairs, for instance, sensilla trichodea. On a morphological basis the sensillae of Gromphadorhina brunneri, were named and classified. Long wavy hairs and large sensory hairs appear to be present also in a related species, G. portentosa, but are lacking in others. Their distribution on the antennae varies greatly from that in G. portentosa but their structure varies only slightly. These two types of sense organs are considered to be specialized forms of sensilla chaetica. They are contact chemoreceptors, as are two other types of sensilla chaetica. Furthermore, thin-walled chemoreceptors are present, such as sensilla trichodea, sensilla basiconica, sensilla coeloconica and a typical mechanoreceptor, the sensillum campaniformium.     

The shape of wind-receptor hairs of cricket and cockroach

We examined the exact shapes of the thread-like wind-receptor hairs in the cricket and cockroach. The diameters of hairs at various distances from the hair tip as measured by scanning electron microscopy revealed unexpected hair shapes. We had expected, a priori, that the shape of the hair would be a slender linearly tapered cone, but the measurements revealed hairs in the form of extremely elongated paraboloids. The diameter of the wind-receptor hairs varies with the square root of the distance from the hair tip, i.e., the diameter rapidly increases with the distance from the tip and is asymptotic to the base diameter. Both the cricket, Gryllus bimaculatus, and the cockroach, Periplaneta americana, showed the same hair shape. In both insects, the formation of the wind-receptor hair during metamorphosis seems to be controlled by a common cytological program. The shape of the hair constrains the mobility of the wind-receptor hair, because both the drag force caused by moving air and the moment of inertia of motion dynamics are functions of shaft diameter. The shape of the hair is a biological trait which affects the sensory information transmitted to the central nervous system. Accepted: 24 February 1998     

Taxonomic and functional implications of stigma morphology in species ofCassia,Chamaecrista, andSenna (Leguminosae:Caesalpinioideae)

Two stigma forms occur inChamaecrista andSenna, but only one inCassia. In the common chambered form, a stigma pore is positioned on the reflexed style tip and is the entrance to a tapering chamber. The pore rim is fringed by hairs which vary in number, size, distribution and shape. In the alternative form the stigma is situated at the apex of the curved style and is crateriform. The crater rim is fringed by hairs of variable number and shape. The stigmatic hairs are predominantly unicellular and cutinized. Stigma and hair differences aid in the taxonomy of the genera. Their functions in pollination biology are discussed.     

Hair density in the Eurasian otter <Emphasis Type="Italic">Lutra lutra</Emphasis> and the Sea otter <Emphasis Type="Italic">Enhydra lutris</Emphasis>

The hair density of adult Eurasian otters Lutra lutra (Linnaeus, 1758) and sea otters Enhydra lutris (Linnaeus, 1758) was analysed using skin samples taken from frozen carcasses. Lutra lutra exhibited a mean hair density of about 70 000 hairs/cm² (whole body, appendages excepted), the mean individual density ranging from about 60 000 to 80 000 hairs/cm². The dominant hair type were secondary hairs (wool hairs), the hair coat comprising only 1.26% of primary hairs (PH). Secondary hair (SH) density remained constant over the body (appendages excepted), whereas a few variations in PH density were observed. Neither an influence of the sex, nor a seasonal variation of the hair coat was found, moulting seems to be continuous. Enhydra lutris had a hair density between 120 000 and 140 000 hairs/cm², the primary hairs representing less than 1% within the hair coat. Hair density remained quite constant over the regions of the trunk but was lower at the head (about 60 000 hairs/cm² on the cheek). The hair follicles were arranged in specific groups with different bundles of varying size, normally comprising dominant numbers of wool hair (SH) follicles. Invariably there was always a large central primary hair follicle and numerous sebaceous glands between the bundles and principally around the PH follicles. The results are discussed related to possible ecological influences on hair coat density.     

Structure,ultrastructure and evolution of floral nectaries in the twinflower tribe Linnaeeae and related taxa (Caprifoliaceae)

Linnaeeae is a small tribe of Caprifoliaceae consisting of six genera and c. 20 species. In Linnaeeae, floral nectaries are located on the corolla‐filament‐tube and nectar is produced from unicellular glandular hairs. We studied 23 taxa using scanning electron microscopy (SEM), light microscopy (LM) and transmission electron microscopy (TEM) and found two distinct nectary morphologies, zonate and gibbous types, and two distinct types of glandular hair, clavate and smooth base types. Plesiomorphic characters associated with the nectary and identified in the tribe include hypocrateriform corollas, dichogamous flowers, zonate nectaries, wet papillate stigmas, vestigial nectary disc and smooth pollen grains. Apomorphic characters include bilabiate corollas, homogamous flowers, bulging nectaries, dry papillate stigmas and echinulate pollen grains. The nectary structure is similar in Vesalea and Linnaea and differs from the rest of the tribe, in accordance with recent phylogenetic results. Nectar secretion is typically granulocrine with subcuticular accumulation of nectar, which we compared with the secretion in multicellular hairs of Adoxa moschatellina. The cuticle on the hair becomes detached from the cell wall and large subcuticular spaces filled with nectar are formed. Nectar is probably released in areas with a thin cuticle. In Zabelia, the smooth basal part of the hair could help to build up the hydrostatic pressure.     

Ultrastructure of the antennal sensilla of the cockroach-egg parasitoid,Tetrastichus hagenowii (Hymenoptera: Eulophidae)

Eggs of a number of cockroach species are parasitized by Tetrastichus hagenowii. The ultrastructure of the sensilla on the antennae of females and males was examined by scanning and transmission electron microscopy. The females have two types of multiporous plate sensilla while the males have only one. Type 1 is found in females and males and has a relatively thin cuticular wall and many pores, while type 2 is found only in females and has a relatively thick cuticular wall and few pores. Both sexes have nonporous, thick-walled, socketed hairs; multiporous, nonsocketed hairs; multiporous, thick-walled pegs; and terminal hairs. In addition, males have multiporous, nonsocketed, long hairs. The sensilla are similar, in many respects, to the sensilla of other chalcid parasitoids. The antennal sensilla of female T. hagenowii are probably involved in ovipositional behavior. The multiporous, long hairs of the male possibly receive stimuli during mating behavior A chemoreceptive function is proposed for the multiporous plate sensilla.     

Freeze-fracture characteristics of insect gustatory and olfactory sensilla

Summary Freeze-fracture data on antennal olfactory and labellar gustatory sensilla of the blowfly Calliphora vicina were compared with those of vertebrate olfactory organs.Insect antennal and vertebrate olfactory axons have similar diameters and show vesicular expansions; insect labellar axons are on average twice as thick and show no vesicular expansions. Vertebrate olfactory and insect labellar and antennal axons display similar intramembranous particle densities. Antennal axons show particle arrangements, resembling tight-junctions. The few extremely thick axons found in labella and antennae show particle arrangements resembling gap-junctions.In regions, proximal to the pores in the insect sensillar hairs, P-faces of olfactory and gustatory cilia show about 200 particles/m². The most proximal and distal portions of the sensory cilia, necklaces and regions in the vicinity of the hair pores respectively, were only encountered in antennal sensilla. P-faces of the ciliary membranes underneath these pores display 1,000–1,200 particles/ m² in unbranched and branched cilia. These values agree with values found in vertebrate olfactory cilia. It is suggested that these high particle densities are related to entities involved in chemoreceptive activities.Accessory cell micropliae have P-face densities of 2,000–3,000 particles/ m², values similar to those found in vertebrate supportive cell microvilli. The membranes of the accessory cells display septate-junctions in areas where these cells overlap themselves, each other and in places where they adhere to the exoskeleton or the basement membrane.     

Morphological synergism in root hair length,density, initiation and geometry for phosphorus acquisition in Arabidopsis thaliana: A modeling approach

Low phosphorus availability regulates root hair growth in Arabidopsis by (1) increasing root hair length, (2) increasing root hair density, (3) decreasing the distance between the root tip and the point at which root hairs begin to emerge, and (4) increasing the number of epidermal cell files that bear hairs (trichoblasts). The coordinated regulation of these traits by phosphorus availability prompted us to speculate that they are synergistic, that is, that they have greater adaptive value in combination than they do in isolation. In this study, we explored this concept using a geometric model to evaluate the effect of varying root hair length (short, medium, and long), density (0, 24, 48, 72, 96, and 120 root hairs per mm of root length), tip to first root hair distance (0.5, 1, 2, and 4 mm), and number of trichoblast files (8 vs. 12) on phosphorus acquisition efficiency (PAE) in Arabidopsis. SimRoot, a dynamic three-dimensional geometric model of root growth and architecture, was used to simulate the growth of Arabidopsis roots with contrasting root hair parameters at three values of phosphorus diffusion coefficient (D _e=1×10^–7, 1×10^–8, and 1×10^–9 cm² s^–1) over time (20, 40, and 60 h). Depzone, a program that dynamically models nutrient diffusion to roots, was employed to estimate PAE and competition among root hairs. As D _e decreased from 1×10^–7 to 1×10^–9 cm² s^–1, roots with longer root hairs and higher root hair densities had greater PAE than those with shorter and less dense root hairs. At D _e=1×10^–9 cm² s^–1, the PAE of root hairs at any given density was in the order of long hairs > medium length hairs > short hairs, and the maximum PAE occurred at density = 96 hairs mm^–1 for both long and medium length hairs. This was due to greater competition among root hairs when they were short and dense. Competition over time decreased differences in PAE due to density, but the effect of length was maintained, as there was less competition among long hairs than short hairs. At high D _e(1×10^–7 cm² s^–1), competition among root hairs was greatest among long hairs and lowest among short hairs, and competition increased with increasing root hair densities. This led to a decrease in PAE as root hair length and density increased. PAE was also affected by the tip to first root hair distance. At low D _e values, decreasing tip to first root hair distance increased PAE of long hairs more than that of short hairs, whereas at high D _e values, decreasing tip to first root hair distance increased PAE of root hairs at low density but decreased PAE of long hairs at very high density. Our models confirmed the benefits of increasing root hair density by increasing the number of trichoblast files rather than decreasing the trichoblast length. The combined effects of all four root hair traits on phosphorus acquisition was 371% greater than their additive effects, demonstrating substantial morphological synergy. In conclusion, our data support the hypothesis that the responses of root hairs to low phosphorus availability are synergistic, which may account for their coordinated regulation.     

Ultrastructural ontogeny of leaf cavity trichomes inAzolla implies a functional role in metabolite exchange

Summary Anabaena azollae is associated with two types of multicellular epidermal trichomes inAzolla leaf cavities, the simple and branched hairs. The observation of transfer cell ultrastructure in some hair cells led to speculation that the cavity hairs might participate in metabolite exchange between the symbionts. The developmental ontogeny of cavity trichomes is described here, using transmission electron microscopy, with a goal of improving our understanding of possible functions of these structures in the symbiosis. The observations have established that all cells of simple and branched hairs develop the structural characteristics of transfer cells, but not simultaneously. Rather, there is an acropetal succession of transfer cell ultrastructure beginning in terminal cells, moving to body cells where present, and ending in stalk cells. The transfer cell stage is followed immediately by senescence in all hair cells. The timing of transfer cell differentiation, considered together with information from other studies, suggests that branched hairs may be involved in exchange of fixed nitrogen between the symbionts, while simple hairs may participate in exchange of fixed carbon fromAzolla toAnabaena. Contribution no. 869 from the Battelle-C. F. Kettering Research Laboratory.     

The elasmobranch spiracular organ

Summary The spiracular organ is a lateral line derived receptor associated with the first gill cleft (spiracle). Its functional morphology was studied in the little skate,Raja erinacea, and a shark, the smooth dogfish,Mustelus canis, with light and electron microscopy. The spiracular organ is a tube (skate) or pouch (shark) with a single pore opening into the spiracle. The lumen is lined with patches of sensory hair cells, and filled with a gelatinous cupula. In the little skate, hair cells form synapses with afferents but apparently not with efferent fibers. In both species, the spiracular organs are deformed by flexion of the hyomandibular cartilage at its articulation with the cranium. The hyomandibula is a suspensory element of the jaws; hyomandibular flexion results in jaw protrusion. The little skate spiracular organ is anchored at one end to the cranium and at the other to the hyomandibula so that it is stretched or relaxed during hyomandibular extension and flexion, respectively. InMustelus, the effects of hyomandibular flexion on the spiracular organ are mediated indirectly by the superior post-spiracular ligament which inserts on the distal end of the hyomandibula. Deformation of the dogfish shark cupula during hyomandibular movement was observed. In the little skate, as revealed by transmission electron microscopy, there is a measurable deflection of the hair cell ciliary bundles from spiracular organs fixed with the hyomandibula in the flexed relative to the extended positions. In both species, hyomandibula flexion should result in hair cell depolarization, and sensory afferent excitation, based on the direction of the observed (skate) or expected (shark) deflection of hair cell cilia.     

The innervation and chemical sensitivity of single aesthetasc hairs

Summary Each aesthetasc hair of the lateral antennule of the California spiny lobsterPanulirus interruptus (Randall) is shown by light and scanning electron microscopy to be innervated by a basally situated cluster of sensory neurons encased in a glial sheath which isolates each cluster from those of other hairs (Figs. 1, 3, 4). The dendrites of these neurons penetrate the aesthetasc hairs and their axons extend to the central nervous system. Extracellular recordings with suction electrodes from the axons of single neuronal clusters were used to determine the responsiveness of individual hairs to a spectrum of amino acids, amines, amides, carbohydrates, carboxylic acids, nucleotides, and a tripeptide (Tables 1, 2, Figs. 6, 8). Randomly selected hairs from the antennules of juvenile, and male and female adult lobsters were shown to be broadly sensitive to a variety of stimuli and are homogeneous in their breadth of responsiveness (Figs. 5, 7). Cluster analysis does not reveal distinct chemoreceptive hair types based on their response spectra, suggesting that the receptor populations of single hairs are uniformly competent to respond to diverse chemical stimuli (Figs. 6, 8). Further, the sensitivity profile of aesthetascs to these stimuli correlates well with behavioral responses ofPanulirus interruptus to these same stimuli (Tables 1, 2).Abbreviation ² Chi-squared     

Morphological and functional heterogeneity in olfactory perception between antennae and maxillary palps in the pumpkin fruit fly,Bactrocera depressa

The morphology and ultrastructure of the olfactory sensilla on the antennae and maxillary palps were investigated through scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and their responses to five volatile compounds were measured using electroantenogram (EAG) and electropalpogram (EPG) techniques in the pumpkin fruit fly, Bactrocera depressa (Shiraki; Diptera: Tephritidae). Male and female B. depressa displayed distinct morphological types of olfactory sensilla in the antennae and maxillary palps, with predominant populations of trichoid, basiconic, and coeloconic sensilla. Basiconic sensilla, the most abundant type of olfactory sensilla in the antennae, could be further classified into two different types. In contrast, the maxillary palps exhibited predominant populations of a single type of curved basiconic sensilla. High‐resolution SEM observation revealed the presence of multiple nanoscale wall‐pores on the cuticular surface of trichoid and basiconic sensilla, indicating that their primary function is olfactory. In contrast, coeloconic sensilla displayed several longitudinal grooves around the sensillum peg. The TEM observation of individual antennal olfactory sensilla indicates that the basiconic sensilla are thin‐walled, while the trichoid sensilla are thick‐walled. The profile of EAG responses of male B. depressa was different from their EPG response profile, indicating that the olfactory function of maxillary palps is different from that of antennae in this species. The structural and functional variation in the olfactory sensilla between antennae and maxillary palps suggests that each plays an independent role in the perception of olfactory signals in B. depressa.     

Structure de l'organe sensoriel apical de l'antenne chez l'Isopode terrestreMetoponorthus sexfasciatus Budde-Lund (Crustacea,Isopoda)

Résumé L'organe sensoriel apical de l'antenne deMetoponorthus a été étudié en microscopie électronique à balayage et par transmission. Il comporte un corps central à la base duquel sont articulées deux longues soies latérales et qui se termine par une touffe de soies très courtes.Les soies de la touffe terminale sont innervées par 4 à 12 neurones bipolaires. Les dendrites traversent le corps central puis pénètrent dans la lumière des soies sans se ramifier. Ils communiquent avec l'extérieur par un pore terminal assez gros. Parmi les dendrites certains paraissent assurer une fonction mécanoréceptrice. Des structures cuticulaires en forme d'écaille protègent la partie terminale des soies du côté axial. Les deux longues soies latérales sont innervées par 5 neurones bipolaires: 4 dendrites pénètrent dans la lumière de la soie; le 5ème, mécanorécepteur, s'arrête au niveau de l'articulation de la soie sur le corps central.La structure fine de cet organe sensoriel apical correspond à celle des chémo-récepteurs de contact connus chez d'autres Arthropodes. Une comparaîson est faite avec les chémorécepteurs de Crustacés marins et terrestres. Chez les formes terrestres on observe un raccourcissement de la partie libre des soies, ainsi qu'une orientation des pores du côté exposé aux stimuli extérieurs. Chez l'Isopode terrestreMetoponorthus étudié dans ce travail, les très courtes soies terminales dépassent à peine du corps central. Le développement des structures cuticulaires au sommet des soies et la tendance des soies à s'intégrer en un organe unique (corps central de l'organe sensoriel) sont autant de spécialisations pour le renforcement de ces soies et leur protection contre la dessication.

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Structure of the apical sensory organ of the antenna in a terrestrial isopod,Metoponorthus sexfasciatus Budde-lund (Crustacea, Isopoda)

Summary The apical sensory organ on the antenna ofMetoponorthus was studied by scanning and transmission electron microscopy. It consists of a tuft of very short terminal hairs which prolongs a central body and two long lateral hairs which are articulated on the central body of the sensory organ.Hairs from the terminal tuft are innervated by 4 to 12 bipolar neurons. The dendritic cilia proceed through the axial body and then enter the lumen of hairs without branching. Dendrites in each hair communicate with environment through a rather wide terminal opening. It is suggested that some dendrites are mechanoreceptive. Scale-like cuticular structures protect the terminal part of the hairs, on the inner side that is not exposed to outer stimuli.The two long lateral hairs are innervated by 5 bipolar neurons: 4 dendrites enter the hair lumen while one, mechanoreceptive, terminates in the socket membrane.The fine structure of this apical sensory organ corresponds to that of known contact chemoreceptors in other Arthropods. A comparison is made with known chemo-receptors in marine and terrestrial Crustacea. In terrestrial forms it can be observed that the hairs become shorter. On the other hand the hair surfaces which are not exposed to outer stimuli show a thickened cuticule. In the terrestrial IsopodMetoponorthus (studied in the present work) the very short terminal hairs barely project past the central body. The development of the cuticular structures at the tip of the hairs and the tendancy of the hairs to be integrated into a single organ (central body of the sensory organ) represent so many adaptations for protection and reduction of evaporation.

     

Light- and electron-microscopic analysis of the statocyst of the American crayfishOrconectes limosus (Crustacea,Decapoda)

Summary The statocyst ofOrconectes limosus contains static hairs arranged in four groups. All the hairs are the same in basic structure; they differ only in length and diameter and in their positions with respect to the other hairs in the group and to the statolith. In terms of functional morphology, each static hair is part of a unit consisting of an acellular lever string, three receptor cells, a scolopale cell, sheath cells, and enveloping cells. The lever string comprises two components in a characteristic longitudinal arrangement. The structure of the receptor cells resembles that of the arthropod chemo- and mechanoreceptors studied previously. The cilium and the postciliary section lie within two receptor cavities, formed by the scolopale cell and the sheath cells; the two cavities communicate with one another. The receptor cells are fixed in position by various structures. Proximally they form desmosomes with the scolopale cell, medially they are joined by filaments to the inner wall of cavity 1, and distally they are retained by a constriction between the two cavities. Two possible stimulus-mediating mechanisms are discussed: pressure changes in the receptor cavities and shearing of the base of the cilia with respect to the preciliary region. The lever string is part of the cuticle and hence is shed during molting. Nevertheless, the statocyst remains functional during this process because new structural units are formed below the old cuticle prior to ecdysis.Abbreviations a axon - b bulb - bb basal body - c cilium - cu cuticle - d dendrite - de desmosome - dm dense material - ec enveloping cell - f fulcrum - h hair - hs hair shaft - ir inner row of hair group - l lingula - ls lever string - m mitochondrion - n nucleus - or outer row of hair group - pcd postciliary dilation - R1 receptor cavity 1 - R2 receptor cavity 2 - rc receptor cell - ro rootlet - s sheath cell - sc scolopale cell - st statoconium - t tooth     

Electrical activity in the chemoreceptors of the blowfly. I. Responses to chemical and mechanical stimulation

The electrical responses of the neurons associated with the various types of chemosensory hairs of the blowfly, Phormia regina Meigen, following stimulation by chemical and mechanical means have been studied. The singly innervated chemosensory hairs on the ovipositor, maxillary palpi, and antennae respond vigorously to chemical stimulation, but not to mechanical stimulation. The triply innervated chemosensory hairs on the labellum, tarsus, and wing have two neurons which respond only to chemical stimuli. The third neuron responds only to mechanical stimulation. The differential responses of the two chemosensory neurons to various chemical stimuli following the removal of the tip of the hair suggest that the structures responsible for chemoreception are located throughout the distal processes of these neurons. The response of the third neuron to mechanical stimulation is similar to the response recorded from the neuron associated with one type of tactile hair which responds to motion and not to steady deformation. Recordings have been made from the neurons associated with purely tactile hairs using the cut hair as an extension of the micropipette. The mechanosensory neuron of the wing chemosensory hair is capable of responding at the rate of at least 600 impulses per sec. and may serve to indicate changes in air flow over the wing surfaces during flight to enable the fly to correct the wing camber and attack angle.