Morphometric estimates of the surface areas of the tracheal and cuticular systems in Peripatus acacioi marcus and marcus (Onychophora)

The surface areas of the tracheal and cuticular systems of Peripatus acacioi individuals of different body weights were determined by morphometric analysis. The results demonstrate that both surfaces increase with body weight, although the observed increase in the surface area of the tracheal system appears to be at a greater rate. The slopes of the two regression lines obtained are statistically different. It is therefore suggested that the preferential route for water loss in P. acacioi is related to the size of the animals, i.e., smaller onychophorans would lose water mainly through the cuticle, while larger ones would lose water through the respiratory surfaces.     

Developing embryo and cyclic changes in the uterus of Peripatus (Macroperipatus) acacioi (Onychophora,Peripatidae)

Female reproductive tracts of the viviparous neo-tropical onychophoran Peripatus acacioi have been examined at different times throughout the year, and the altering relationship between the developing embryo and the uterus is described. Depending on her age and time of year, the female may have one or two generations of embryos within her uterus. The uterine wall consists of a thin outer epithelium and basal lamina, three layers of muscles, and a thick basal lamina beneath an inner epithelium lining the uterus lumen. These layers are consistent along the length of the uterus apart from the inner epithelial lining, which varies according to position in the uterus and the developmental stage of embryos contained in the uterus. Early embryos are positioned along the length of the uterus and therefore have space in which to grow. During cleavage and segment formation, each embryo is contained within a fluid-filled embryo cavity that increases in size as the embryo grows. Morulae and blastulae are separated by lengths of empty uterus in which the epithelial lining appears vacuolated. Until the process of segment formation is complete, the embryos are attached to a placenta by a stalk and remain in the same part of the upper region of the uterus. As these embryos grow, the lengths of vacuolated cell-lined uterus between them decrease. Each embryo cavity is surrounded by the epithelial sac, the maternal uterine epithelium, which becomes overlaid by a thin layer of cells, the embryo sac, which is believed to be of embryonic origin. The placenta is a syncytial modification of the epithelial sac located at the ovarian end of each embryo cavity covered by the embryo sac and is analogous to the mammalian noninvasive epitheliochorial placenta. Segment-forming embryos have their heads directed toward the ovary. As the embryo gets longer during segment formation, its posture changes from coiled to flexed. Once segment formation is complete, the embryo loses contact with its stalk, an embryonic cuticle forms, and the embryo turns around so that its head is directed toward the vagina. The embryo escapes from its embryo sac and moves to the lower part of the uterus. In the lower part of the uterus, the straightened fetuses are first unpigmented but subsequently become pigmented as the secondary papillae on the body surface form and an adult-type cuticle forms beneath the embryonic cuticle. While the embryos are contained within their embryo cavities, nutrients are supplied by the placenta. Throughout development the mouth is open and in the mature fetus the gut is lined by peritrophic membrane and material is present in the gut lumen. Trachea have been observed only in fetuses that were ready for birth. Insemination, cyclical changes in the uterine epithelium, and the nature of the cuticle shed at parturition are discussed. © 1995 Wiley-Liss, Inc.     

An ultrastructural study of the cuticle in the marine annelid Heterodrilus (Tubificidae, Clitellata)

The ultrastructure of the cuticle in four species of the marine Heterodrilus (H. paucifascis, H. pentcheffi, H. flexuosus, H. minisetosus) is investigated with transmission electron microscopy. The noncellular cuticle consists of several parts; closest to the epidermis is a thick zone of collagen fibers embedded in a matrix. The matrix continues outside the fiber zone, forming a layered epicuticle. The external surface of the epicuticle is covered by evenly distributed, membrane-bound bodies, termed epicuticular projections. The epicuticular projections have their longitudinal axis perpendicular to the surface of the cuticle and are attached to the surface by either the surrounding membrane itself or by short pedestals. Microvilli, extensions from the epidermal cells, penetrate and sometimes pass completely through the cuticle. There is interspecific variation in the morphology of the cuticle. The four studied species differ in the arrangement of the collagen fibers, from irregularly distributed fibril bundles to orthogonally arranged fiber layers, as well as in the number and density of layers in the epicuticle. One of the studied species, H. paucifascis, shows intraspecific variation, which is associated with sample locality. The Bahamian specimens of H. paucifascis have four layers in the epicuticle, club-shaped epicuticular projections, and collagen fibers forming a less defined orthogonal grid, while the Belizean specimens have three layers in the epicuticle, epicuticular projections with a bulging part at midlevel, and a distinct orthogonal grid. Based on these findings the variation in the morphology of the cuticle appears to be dependent on both phylogenetic constraints, and functional and environmental factors.     

An examination of surface epithelium structures of the embryo across the genus Poeciliopsis (Poeciliidae)

In viviparous, teleost fish, with postfertilization maternal nutrient provisioning, embryonic structures that facilitate maternal‐fetal nutrient transfer are predicted to be present. For the family Poeciliidae, only a handful of morphological studies have explored these embryonic specializations. Here, we present a comparative morphological study in the viviparous poeciliid genus, Poeciliopsis . Using microscopy techniques, we examine the embryonic surface epidermis of Poeciliopsis species that vary in their level of postfertilization maternal nutrient provisioning and placentation across two phylogenetic clades and three independent evolutionary origins of placentation. We focus on surface features of the embryo that may facilitate maternal‐fetal nutrient transfer. Specifically, we studied cell apical‐surface morphology associated with the superficial epithelium that covers the body and sac (yolk and pericardial) of embryos at different developmental stages. Scanning electron microscopy revealed common surface epithelial cells across species, including pavement cells with apical‐surface microridges or microvilli and presumed ionocytes and/or mucus‐secreting cells. For three species, in the mid‐stage embryos, the surface of the body and sac were covered in microvillus epithelium. The remaining species did not display microvillus epithelium at any of the stages examined. Instead, their epithelium of the body and sac were composed of cells with apical‐surface microridges. For all species, in the late stage embryos, the surface of the body proper was composed of apical‐surface microridges in a “fingerprint‐like arrangement.” Despite the differences in the surface epithelium of embryos across Poeciliopsis species and embryonic developmental stages, this variation was not associated with the level of postfertilization maternal nutrient provisioning. We discuss these results in light of previous morphological studies of matrotrophic, teleost fish, phylogenetic relationships of Poeciliopsis species, and our earlier comparative microscopy work on the maternal tissue of the Poeciliopsis placenta.     

Fine structure of the cuticle of the black widow spider with reference to surface lipids

The surface and transverse sections of the cephalothorax, abdomen, and walking leg cuticle of the black widow spider, Latrodectus hesperus, were examined by scanning and transmission electron microscopy. Cuticle that was untreated prior to normal EM preparative procedures was compared with cuticle subjected to lipid solvents and/or concentrated alkali. The surface of untreated dorsal cephalothorax cuticle contained droplets and a lipid film that obscured fine surface detail. Immersing the cuticle in chloroform: methanol removed the droplets and lipid film, exposing previously covered openings to dermal gland ducts. An epicuticle, exocuticle, and endocuticle were present in all transverse sections of cuticle as was a complex system of pore and wax canals that connected the epidermis with the cuticle surface. The epicuticle of the walking leg was composed of three sublayers: outer membrane, outer epicuticle, and the dense homogeneous layer. A cuticulin layer was not observed. Lipid solvents did not significantly alter the morphology of any of these layers or the contents of the wax/pore canals.     

Ultrastructure, development, and homology of insect embryonic cuticles

Ultrastructure and deposition of the cuticles secreted by embryos representing eight insect orders were examined by transmission and scanning electron microscopy. Embryos of the apterygote silverfish Thermobia domestica deposit two embryonic cuticles. Deposition of the first (EC1) is initiated at the beginning of appendage development when the intercalary segment and the neural groove are clearly visible. This cuticle lacks surface microsculpture and consists of an outer epicuticle and an underlying fibrous layer, thought to represent procuticle. At the time of dorsal closure, deposition of a second embryonic cuticle (EC2) begins; this bears sensilla and functions in the first instar larva. In representative embryos of seven pterygote orders (Ephemeroptera, Odonata, Plecoptera, Neuroptera, Coleoptera, Lepidoptera, and Mecoptera), three cuticles were found to be secreted. The first cuticle in pterygotes is homologous to EC1 of T. domestica, but consists solely of outer epicuticle. EC2, the "prolarval cuticle," bears a characteristic surface microsculpture in embryos of some species and egg-teeth and other hatching devices, and consists of outer and inner epicuticles and a more or less reduced procuticle. EC2 is reduced in the embryos of derived endopterygotes, where a procuticle is lacking and the inner epicuticle is reduced. After hatching, when EC2 is shed, the first instar larva is covered by a third embryonic cuticle (EC3), whose deposition was initiated while the insect was still within the egg. Presence of only two embryonic cuticles in cyclorrhaphous flies is due to the total loss of prolarval cuticle. Investigated exopterygote and endopterygote insects excluding flies thus deposit three embryonic cuticles, and their juveniles (exopterygote "nymphs"; endopterygote "larvae") seem to hatch at equivalent stages of development. Differences between the modes of cuticulogenesis in silverfish and pterygote embryos suggest that the apterygote first larval instar was embryonized and became a fully embryonic prolarva in pterygotes.     

Formation of cytoskeletal elements during mouse embryogenesis. IV. Ultrastructure of primary mesenchymal cells and their cell-cell interactions

The ultrastructure of the day 8.5 mouse embryo has been studied by transmission electron microscopy, with special emphasis on the primary mesenchymal cells and their interaction with cells of the embryonic ectoderm and the proximal endoderm. The organization of the two polar epithelial cell layers (embryonic ectoderm and proximal endoderm), the isolated cells of the distal endoderm and the primary mesenchymal cells is described. Primary mesenchymal cells are different from embryonic ectoderm cells, from which they are derived, not only by the absence of desmosomes and intermediate-sized filaments of the cytokeratin type but also by their variable morphology not exhibiting stable polar architecture, and their numerous cytoplasmic processes which make contacts with the basal lamina of the ectoderm, the basal cell surface of the proximal endoderm, and other mesenchymal cells. Over most of the embryo the embryonic ectoderm is covered by a typical basal lamina, except for certain regions that are frequently characterized by cytoplasmic projections ("blebs') from the basal cell surface membrane. In contrast, the basal surface of the proximal endoderm is not covered by a continuous basal lamina and reveals mushroom-like protrusions of the cortical cytoplasm. Junctions between primary mesenchymal cells are numerous and include adhaerens-type formations of various sizes as well as gap junctions. Occasionally, a special type of junction between mesenchymal cells and embryonic ectoderm has been found, resulting in local interruptions of the basal lamina. The observations are discussed in relation to possible mechanisms of mesoderm formation and the drastic changes of cell character that accompany this process, including cytoskeletal changes such as the disappearance of cytokeratin filaments and the expression of vimentin.     

Fine structure and development of the cuticle of Intoshia variabili (Orthonectida)

The body of free-swiming mature Intoshia variabili (Orthonectida) is covered by a thin cuticle, 0.3 μm thick. The cuticle is formed at the time when the orthonectid embryos develop in the plasmodium. The process of cuticle formation begins just after the first cilia begin to appear at the surface of the ciliated cells. At first, small extensions of the cell membrane appear at the surface of the cell, more or less parallel to the cell surface. As they develop futher, they stand up, and amorphic material begins to appear between them. The extensions then become microvilli and obtain their final shape, with a small subdistal swelling and a narrower distal part. They are situated very regularly on the surface of the cell. After the microvilli have obtained their final form, material between them begins to get its final structure typical of the adult form. During the period when the mature orthonectid begins to leave the plasmodium and emerge from the host, the regular microvilli begin to disappear, and only small irregular extensions are present under the cuticle on the surface of the cell. During the process of cuticle formation a large amount of smooth endoplasmic reticulum develops in the cells, but once the cuticle is formed it gradually disappears.     

Embryonic development of a whirligig beetle,Dineutus mellyi,with special reference to external morphology (insecta: Coleoptera,Gyrinidae)

The egg morphology and successive changes of developing embryos of the whirligig beetle, Dineutus mellyi (Adephaga: Gyrinidae) are described from observations based on light and scanning electron microscopy. The egg surface is characterized by minute conical projections covering the entire egg surface, a stalk‐like micropylar projection at the anterior pole of the egg, and a longitudinal split line along which the chorion is cleaved during the middle embryonic stages. The germ band or embryo is formed on the ventral egg surface, and develops on the surface throughout the egg period; thus, the egg is a superficial type, as is the case in most coleopteran species. A pair of lateral tracheal gills (LTGs) of the first abdominal segment originates from appendage‐like projections arising at the lateral side of pleuropodia, and the LTGs of the second to ninth abdominal segments are arranged in a row with that of the first segment. Therefore, LTGs are structures with serial homology. The paired dorsal tracheal gills (DTGs) of the ninth abdominal segment are formed on the regions just latero‐dorsal to the LTGs of this segment. Regarding the pleuropodia as the structures being homologous with thoracic legs, neither the LTGs nor DTGs are homologous with thoracic legs, but originate in the more lateral region corresponding to the future pleura of the thoracic segments. The last (10th) abdominal segment in the larva is formed by the fusion of the embryonic 10th and 11th abdominal segments. Four terminal hooks at the end of the last abdominal segment originate from two pairs of swellings on the posterior end of the embryonic 11th abdominal segment. It is proposed that the terminal hooks possibly correspond to the claws of medially fused cerci of the embryonic 11th abdominal segment. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.     

Formation of cytoskeletal elements during mouse embryogenesis

Abstract. The ultrastructure of the day 8.5 mouse embryo has been studied by transmission electron microscopy, with special emphasis on the primary mesenchymal cells and their interaction with cells of the embryonic ectoderm and the proximal endoderm. The organization of the two polar epithelial cell layers (embryonic ectoderm and proximal endoderm), the isolated cells of the distal endoderm and the primary mesenchymal cells is described. Primary mesenchymal cells are different from embryonic ectoderm cells, from which they are derived, not only by the absence of desmosomes and intermediate-sized filaments of the cytokeratin type but also by their variable morphology not exhibiting stable polar architecture, and their numerous cytoplasmic processes which make contacts with the basal lamina of the ectoderm, the basal cell surface of the proximal endoderm, and other mesenchymal cells. Over most of the embryo the embryonic ectoderm is covered by a typical basal lamina, except for certain regions that are frequently characterized by cytoplasmic projections ('blebs') from the basal cell surface membrane. In contrast, the basal surface of the proximal endoderm is not covered by a continuous basal lamina and reveals mushroom-like protrusions of the cortical cytoplasm. Junctions between primary mesenchymal cells are numerous and include adhaerens-type formations of various sizes as well as gap junctions. Occasionally, a special type of junction between mesenchymal cells and embryonic ectoderm has been found, resulting in local interruptions of the basal lamina. The observations are discussed in relation to possible mechanisms of mesoderm formation and the drastic changes of cell character that accompany this process, including cytoskeletal changes such as the disappearance of cytokeratin filaments and the expression of vimentin.     

Ultrastructure of the tube-foot of an ophiuroid echinoderm, Hemipholis elongata

The morphology of the tube-foot of the brittlestar, Hemipholis elongata was examined by transmission and scanning electron microscopy. The entire surface of the tubefoot is covered by microvilli and a thick cuticle layer. At the tip of the tube-foot the cuticle layer is thinner and sensory-secretory complexes are seen. These are composed of two secretary cells and a central ciliated sensory cell. Scanning electron microscopy shows that the cilium which extends from the receptor cell ends flush with the surrounding microvilli. These studies suggest that the tube-feet in ophiuroids are important structures in sensory-reception, gasexchange as well as locomotion. The hemoglobin containing cells within the lumen of the tubefeet may serve in oxygen transport and storage.     

Sensilla on the palps and legs of the adult soft tick argas persicus oken (IXODOIDEA: ARGASIDAE) and their projections to the central nervous system

The sensory structures present on the palps and legs of adult Argas persicus Oken (Ixodoidea: Argasidae) were studied by light, scanning and transmission electron microscopy. The number, distribution, surface morphology and the fine structure of the prominent sensilla present on these appendages were determined. The palps have 2 morphologically prominent types of sensilla: one with a grooved surface of the hair and the other having a non-grooved hair. The TEM distinguishes at least 4 prominent subtypes in grooved sensilla with single or double lumina and dendrites occupying the periphery of the central lumen or distributed all over the central lumen. Amongst the sensilla with non-grooved hair-shaft, a rare type of Olfactory Mechanoreceptive (OM) sensillum was found on the palps and the first legs of A. persicus. At the base of the hair-shaft, the OM sensillum has 2 mechanosensory dendrites. The hair-shaft of the sensillum has a porous cuticle, characteristic of an olfactory sensillum. The lumen of the hair-shaft is invested with branching dendrites from 3–8 neurons, which are surrounded by 4 sheath cells. The sensilla on the legs, including those present in the Hallers organ, are of at least 3 prominent categories. (i) Single wall with un-innervated hair-shaft. (ii) Single wall, multiporous sensillum with dendrites present in the hair shaft. (iii) Double walls with spoke channels and dendrites present in the central lumen. Sensory projections from the crown of sensilla located on the distal end of the palp extend to the palpal and suboesophageal (SOG) ganglia. Projections in the SOG extend further to the contralateral side. Sensilla in the Hallers organ project to the first pedal ganglion and to the anterodorsal region of supraoesophageal ganglion. As expected, the primary sensory projections from the sensilla of the other 3 legs extend to the respective pedal ganglia.     

The fate of surface cell layers of Daucus carota (L.) embryos raised in suspension culture

The ultrastructure and fate of surface cells covering mature somatic embryos of Daucus carota grown in suspension culture were analyzed and new information obtained concerning somatic embryogenesis in these conditions. Our studies showed that during some developmental stages, these embryos were covered irregularly and discontinuously by cells with a typical protodermal phenotype characterized by a cuticle on the outer cell wall. We observed that cells with cuticles were peeled off from the surface of mature embryos. Before peeling off, these cells underwent programmed cell death, which was confirmed by the TdT-mediated dUTP nick end labeling method. Transmission electron microscopy revealed advanced processes of autophagy in these cells.     

Cycles embryonnaires et sécrétion de la cuticule chez l'embryon de blatte, Blabera craniifer

Cuticle deposition has been studied with the electron microscope in cockroach embryos (Blabera craniifer) during normal incubation in situ and in culture in vitro, in the absence or presence of inokosterone (a phytoecdysone).Two cuticles are deposited successively during embryonic life, respectively between stages 11 and 17, and stage 21 and 24 hr after hatching. The occurrence of two embryonic cycles is thus demonstrated, the first ending at stage 17 without exuviation since there is no old cuticle to be shed, the second one at hatching.In embryos explanted at stage 17 and cultured in vitro, the formation of cuticle 2 occurred at the same rate as in situ. The addition of inokosterone (50 μg/ml) to the medium resulted in the early onset of cuticle deposition (in 3 days as compared with 15 days in situ) in legs previously cut at the base of the tarsus. Cuticle 2 was completed within 9 days after explantation (as compared with about 20 days elapsing in the normal embryo between stage 17 and the completion of cuticle 2). Unsectioned appendages were insensitive to the hormone.Regeneration of sectioned legs, which occurred normally n vitro in non-treated embryos, was completely inhibited in the presence of inokosterone, presumably because the hormone caused early immobilization of cells through accelerated cuticle formation.Results suggest that embryonic cycles are controlled by the same hormonal mechanism as larval cycles.     

Ultrastructure of the antennal sensilla of aphids

Summary An electron microscopical study was made of the coeloconic and placoid sensilla on the antennae of the aphids Aphis pomi, Macrosiphum euphorbiae, Nasonovia ribis-nigri, and Pemphigus bursarius. Scanning electron microscopy revealed some variation in morphology which may be functionally important but is more likely to reflect the evolution of these species.The placoid sensilla were shown by transmission electron microscopy to have the same basic structural pattern. Each group of two or three neurons is surrounded by two ensheathing cells. The ciliary regions of the dendrites pass through a vacuole into a cavity between an outer and an inner cuticle where they may be connected to the dendritic branches although such connections were not seen. Small pores (8 nm diameter) partially penetrate the cuticle implying that these sensilla have an olfactory function. They are suggested to be important in host selection by alate aphids.The coeloconic sensilla are poreless pegs with nonsensory cuticular projections at their tips. The distal portions of their dendrites contain densely packed microtubules and the cellular arrangement of the sensilla is similar to that of the placoid sensilla. It is suggested that they may function as thermoreceptors.The authors thank the Long Ashton Research Station, Bristol for use of the SEM facilities. A.K. Bromley gratefully acknowledges the tenure of a S.R.C. CASE Studentship and thanks Professor L.H. Finlayson for research facilities     

Egg envelopes and cuticle renewal in Porcellio embryos and marsupial mancas

An important adaptation to land habitats in terrestrial isopod crustaceans is development of embryos in a fluid-filled female brood pouch, marsupium. The study brings insight into the structure and protective role of egg envelopes and cuticle renewal during ontogenetic development of Porcellio embryos and marsupial mancas. Egg envelopes cover embryos, the outer chorion until late-stage embryo and the inner vitelline membrane throughout the whole embryonic development. Egg envelopes of Porcellio have relatively simple ultrastuctural architecture compared to Drosophila egg envelopes. Exoskeletal cuticle is produced in late embryonic development by hypodermal cells of the embryo and is renewed in further development in relation to growth of developing embryos and mancas. Cuticle structure and renewal in prehatching late-stage embryos and marsupial mancas exhibit main features of cuticle in adults. Epicuticle is thin and homogenous. The characteristic arrangement of chitin-protein fibers and the dense distal layer in exocuticle are hardly discernible in prehatching embryo and distinct in marsupial mancas. Endocuticle consists of alternating electron dense and electron lucent sublayers and is perforated by pore canals in both stages. Differences from adult cuticle are evident in cuticle thickness, ultrastructure and mineralization. Signs of cuticle renewal in prehatching embryo and marsupial mancas such as detachment of cuticle from hypodermis, partial disintegration of endocuticle and assembly of new cuticle are described.     

Revising the definition of the crustacean seta and setal classification systems based on examinations of the mouthpart setae of seven species of decapods

The crustacean cuticle has numerous projections and some of these projections, the setae, have important mechanical as well as sensory functions. The setae display a wide diversity in their external morphology, which has led to great problems separating setae from other projections in the cuticle and problems in making a consistent classification system. Here, the cuticular projections on the mouthparts of seven species of decapods are examined by scanning and transmission electron microscopy. A new definition is given: a seta is an elongate projection with a more or less circular base and a continuous lumen; the lumen has a semicircular arrangement of sheath cells basally. From the details of the external morphology the mouthpart setae are divided into seven types: pappose, plumose, serrulate, serrate, papposerrate, simple and cuspidate setae, which are suggested to reflect mechanical functions and not evolutionary history. This classification system is compared with earlier systems.  © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society , 2004, 142 , 233–252.     

Comparative ultrastructural study of the cuticle and spermatozoa in Propappus volki Michaelsen, 1916 (Annelida: Clitellata)

The ultrastructure of the cuticle and mature spermatozoa of the oligochaete Propappus volki Michaelsen, 1916 is described with the aim of providing additional data for clarifying the systematic position of the taxon. P. volki is a fresh-water species living in streams, and is easily recognized by its proboscis on the pre-segmental prostomium and, in mature specimens, by a clitellum covering the segments XII–XIV. The cuticle is composed of a proximal fibre zone and a distal layered epicuticle covered with membrane-bound epicuticular projections. The fibre zone consists of collagenous fibres in a matrix, arranged in either densely packed parallel layers with the fibres oriented in the same direction, or with more loosely distributed fibres, although with the same main orientation. The epicuticular projections are pyramidal with the base leaning on the outer surface of the epicuticle. The cuticle covering the proboscis differs in morphology from that of the rest of the worm; the fibre zone is composed of thin and short fibrils running in all directions, and the epicuticular projections are longer and more narrow than the projections in other regions of the worm.

The spermatozoa are filiform cells formed, in sequence, by an acrosome, an elongated nucleus, a long midpiece, and a flagellum. The acrosomal tube is short and straight with a completely external acrosomal vesicle. Following the acrosome is a apically corkscrew-shaped and basally straight nucleus. The midpiece is twisted and formed by five mitochondria. The flagellum shows a prominent central sheath arrangement.

A comparison with ultrastructurally described cuticles and spermatozoa from other clitellate species reveals most similarities with enchytraeids.     

Appendage development in embryos of the oribatid mite Archegozetes longisetosus (Acari, Oribatei, Trhypochthoniidae)

The development of reliable techniques to provide large numbers of fixed mite embryos free of their tough membranes has allowed us to produce scanning electron micrographs of oribatid embryos for the first time. Antibody staining for expression of the gene Distal-less demonstrates the formation of the labrum from a pair of regions in the ocular lobes, indicating a possible appendicular origin for the labrum. The chelicerae are followed from their initial postoral position through their anterior rotation to become preoral. The pedipalpal lobe, involved in the formation of the gnathosoma, is shown to be almost the size of the pedipalp at some stages, as well as expressing Distal-less . The fourth pair of walking limbs are not present in oribatid prelarvae and larvae, however, their anlage are visible in later embryonic stages but these do not express the gene Distal-less , suggesting that formation of distal structures is suppressed at this stage. Claparède's organs, present between coxae of legs I and II of larvae, are shown for the first time unequivocally to derive from the base of legs II. These are proposed to be homologous to the lateral organs of other arachnid groups.     

Structure of the cuticle of the common house cricket with reference to the location of lipids

Cuticle segments from the thorax, abdomen, and jumping legs of the house cricket. Acheta domesticus, were examined using histological techniques for light microscopy, scanning and transmission electron microscopy, and direct examination of frozen-fractured cuticle. The surface of untreated cuticle is covered by a lipid film which obscures fine surface detail. Standard EM preparative procedures, as well as washing the cuticle with ethanol before examination, remove this film exposing previously covered openings to dermal gland ducts and wax canals. An epicuticle, exocuticle, mesocuticle, endocuticle, and a deposition layer were present in all transverse sections of cuticle. Light microscopy showed that the exocuticle and mesocuticle are heavily impregnated with lipids, whereas there is little lipid associated with the endocuticle. Frozen-fractured cuticle clearly shows the ‘plywood’ structure of the meso- and endocuticle, while the exocuticle fractures as if it were a solid sheet. The epicuticle is composed of a dense homogeneous layer, cuticulin, outer epicuticle, and the outer membrane. Superficial wax was detected only in cuticle samples prepared using vinylcyclohexane dioxide as a polar dehydrant. The results were used to construct a comprehensive model of the cuticle of A. domesticus.