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.     

PORE CANALS AND RELATED STRUCTURES IN INSECT CUTICLE

The fine structure and the distribution of an esterase have been studied in the cuticle of Galleria larvae, Tenebrio larvae and pupae, and in the wax-secreting cuticle of the honey bee, and compared with those in the cuticle of the caterpillar of Calpodes. In Galleria and Tenebrio the pore canals are spaces passing through the lamellate endocuticle from the epithelium to the epicuticle. They contain a filament from the cells which may be concerned in their formation. The shape of the pore canal is probably determined by the orientation of the fibres making up the lamellae in the endocuticle and is not a regular helix. The pore canals also contain numerous filaments of another sort which pass on through the epicuticle and are believed to be the origin of the surface wax. They are particularly abundant in the pore canals of the honey bee wax-secreting cuticle and extend into the cell in long pockets surrounded by an envelope of the plasma membrane. The esterase is probably concerned with the final stage of wax synthesis, for its distribution is similar to that of the lipid filaments.     

Cilia and other surface structures of the trochophore of Harmothoë imbricata (Polychaeta)

Summary Ciliary aggregations occur as the prototroch, neurotroch, apical system and as tufts associated with the eyes and superficial glands. The major collection of cilia is the locomotory organ or prototroch that runs around the equatorial plane of the larva. This band is composed of four contiguous rows of cells, the two medial rows bearing the long locomotory cilia. The cilia occur in clumps, with several clumps arising from each prototroch cell while both the main cells contribute to each clump. The central filaments of these cilia are orientated at right angles to the long axis of the clump, the direction of ciliary beat being at right angles to the progression of the metachronal wave along the prototroch. The neurotroch, extending from the mouth to the posterior pole of the larva, beats away from the mouth. The rate of beating is rapid, and the cilia are short. The apical area of the larva is bordered by five single lines of compound cilia that surround a few stiff cilia. All the cilia beat occasionally. A further line of cilia, the akrotroch, exists at a position halfway between the apical area and the prototroch on the same side as the mouth. These cilia beat towards the prototroch. Some of these cilia are associated with sets of glandular openings. The fine structure of the glands and cuticle is described. The glands are small mucous glands that open via a projecting pore which is encircled by rings of microvilli. They often occur in groups of four or in pairs. The cuticle is similar to that described previously for adult polychaetes.This work was started under a Science Research Council (U.K.) grant (B/SR/1871) for a Research Assistantship to Dr. M. S. Laverack and grateful acknowledgement is made for this. We would like to thank Dr. A. Boyde for all his advice and use of apparatus. The scanning electron microscope used in this study was provided by a Science Research Council (U. K.) grant to Dr. Boyde. We would like to thank Mrs. J. Parkes for photographic assistance.     

Structure of the cuticle of the alpine weta,Hemideina maori (Saussure) (Orthoptera: Stenopelmatidae)

Sclerotized cuticle segments from the thorax, dorsal abdomen, and ventral abdomen of the alpine, weta Hemideina maori (Saussure) (Orthoptera: Stenopelmatidae) were examined by light microscopy and by scanning and transmission electron microscopy. An epicuticle, exocuticle (outer and inner), mesocuticle, endocuticle, and deposition layer are present in transverse sections. The epicuticle is further composed of a cuticulin layer and inner epicuticle, the latter being finely laminated and containing narrow wax canals that terminate below the cuticle surface. Openings to dermal gland ducts are visible on the surface as are large setae and smaller sensory pegs. Frozen fractured cuticle reveals the presence of horizontal ducts or channels that run laterally within the cuticle. The structure of weta cuticle is compared with that of the common house cricket and arthropods in general.     

Ultrastructure of the nymphal integument in the camel tick Hyalomma (Hyalomma) dromedarii (Ixodoidea: Ixodidae)

The ultrastructure of the nymphal integument in the ixodid tick Hyalomma (Hyalomma) dromedarii is compared for stages of development during and after feeding, and up to the first step of molting, apolysis. The integument comprises a cuticular layer and underlying epidermal cells. The body cuticle, which consists of both sclerotized and non-sclerotized parts, is divided into an outer, thin epicuticle, and an inner, thick, fibrillar procuticle. Pore canals in the procuticle are continuous with wax canals which traverse the epicuticle. As feeding progresses, the parallel, extensible epicuticular folds disappear due to the gut filling with ingested blood. The procuticular zone, however, becomes subdivided into an exocuticle, similar to the previously seen procuticle, and a lamellate endocuticle. Pore canals lose their parallel pattern and appear to have become deformed by stretching of the cuticle. The flat epidermal cells grow asynchronously during feeding; their cytoplasm becomes packed with well-developed rough endoplasmic reticulum (RER), while the cell apices project long microvilli extending deep into the procuticle. The RER undergoes ultrastructural changes indicating synthetic activity. Dense material released through the microvilli may serve to lyse the endocuticle and thus cause separation of the cuticle from the epidermis during apolysis. The lysed area, the exuvial cavity, is filled with lysed components which are probably withdrawn by endocytosis into the apical coated vesicles which appear in epidermal cells. Two types of integumental glands, which may participate in wax production, are observed in this study. The ultrastructure of their previously undescribed cuticular ducts is described, in addition to other hypodermal structures including epidermis-muscle attachments and sensory receptors.     

Ultrastructure of the wax-gland system in subterranean scale insects (homoptera,coccoidea, margarodidae)

The ultrastructure of wax glands (integumentary, stigmatic, and peristigmatic glands) was investigated in larvae, cysts, and adult females and males of species belonging to the genera Porphyrophora, Sphaeraspis, and Eurhizococcus. The general organization and cytological characteristics are similar for all glands studied. Each gland is composed of a single layer of 8 to 40 cells. The glandular cells are characterized by a very large quantity of smooth endoplasmic reticulum which forms dense zones throughout the cytoplasm, but is always placed near the collecting canals in the presence of mitochondria. Each cell has a central canal reservoir which penetrates it deeply and gives rise to a large number of lateral collecting canals, formed by the invagination of the apical plasma membrane. The canals open into a subcuticular cavity forming a common reservoir in which the secretion is accumulated. This reservoir is covered by a modified cuticle formed from the endocuticle and the epicuticle. The endocuticle is composed of a network of fine tubular structures and has many filaments on its surface. The epicuticle is perforated by numerous pores. There is no cuticular duct. The secretion crosses the cuticle in three successive steps. First, it passes through the filaments, then through fine tubular structures of the endocuticle, and finally through the epicuticular pores.     

Structure of the sex pheromone-producing prothoracic glands of the male old house borer,Hylotrupes bajulus (L.) (Coleoptera : Cerambycidae)

Pheromone glands were discovered in the prothorax of male Hylotrupes bajulus (L.) (Coleoptera : Cerambycidae). These exocrine glands were investigated by SEM and light microscopy. Almost the entire prothorax is internally lined with a glandular matrix composed of numerous heap-like complex glands. Each gland is divided into several subunits (“pore field units”), which in turn are composed of a varying number of glandular units. The glandular unit comprises a distal voluminous glandular cell, a medial (intercalary) canal cell I, and a minute canal cell II near the cuticle. The spindle-like, basally constricted receiving canal of the gland cell leads into the long, non-porous conducting canal, which, by a single cuticle canal, opens in an external pore field, an aggregate of orifices of other such cuticle canals. In varying numbers, these randomly arranged pore fields are located in superficial pits that are distributed over nearly the entire prothorax. The structure of these male sex pheromone glands is discussed in comparison with other known glands in species of Coleoptera characterized by multicellular aggregations and by pore plates.     

CUTICLE DEVELOPMENT ON GLANDULAR TRICHOMES OF CANNABIS SATIVA (CANNABACEAE)

The dermal sheath of glandular trichomes of Cannabis sativa L., consisting of cuticle and a subcuticular wall, was examined by transmission electron microscopy. Cuticle thickened selectively on the outer wall of disc cells of each trichome prior to formation of the secretory cavity, whereas thickening was less evident on the dermal cells of the bract. Membraned secretory vesicles that differ in size and appearance in the secretory cavity were the source of precursors for synthesis of cuticle. Vesicle contents, released following the degradation of the vesicle membrane upon contact with the subcuticular wall, contributed to both structured and amorphous phases of cuticle development. The structured phase was represented by deposition and thickening of cuticle at the subcuticular wall-cuticle interface to form a thickened cuticle. In the amorphous phase precursors permeated the cuticle in a liquid state, as shown by fusion of cuticles and wax layers between contiguous glands, and may have contributed to growth in surface area of the expanding sheath. Disc cells are interpreted to control growth of secretory cavity by secretion of membraned vesicles into the cavity. The thickened cuticle, which increased eightfold in thickness during enlargement of the gland, provided structural strength for the extensive surface area of the dermal sheath. The gland of Cannabis in which vesicle contents contribute to the growth in thickness and surface area of the cuticle of the sheath is interpreted to represent a phylogenetically derived state as contrasted to secretory glands possessing only cuticle and lacking a complement of secretory vesicles.     

Fine structure of the epicuticle of the desert scorpion, Hadrurus arizonensis, with reference to location of lipids.

The surface and transverse sections of the epicuticle of the desert scorpion, Hadrurus arizonensis, were examined by scanning and transmission electron microscopy, respectively. Sclerite cuticle that was untreated prior to normal EM preparative procedures was compared to cuticle subjected to lipid solvents, high temperature, and concentrated alkali. Surface morphology of untreated intersegmental cuticle was also examined. The epicuticle is composed of four sublayers: outer membrane, outer epicuticle, cuticulin, and the dense homogeneous layer. Lipid solvents did not significantly alter the morphology of any of these layers or the contents of the wax canals that penetrate the cuticulin layer even though the solvents effectively remove lipids from the epicuticle for chemical analysis. The surface of the sclerite cuticle contains amorphous particles, crystalline projections, and scattered openings to dermal gland ducts. Perforations that correspond to the opening of wax canals were faintly visible after extraction of surface waxes and clearly visible after KOH treatment. No openings to dermal gland ducts or wax canals were observed in untreated intersegmental cuticle. However, wax canals are likely obscured by surface waxes similar to those present in sclerite cuticle.     

Fine structure of the sensilla of Peripatopsis moseleyi (Onychophora)

Summary Three types of sensilla occurring on the lips and on the antennae of Peripatopsis moseleyi have been investigated by scanning and transmission electron microscopy. On the lips sensory spines can be found which contain numerous cilia originating from bipolar receptor cells. They reach the tip of the spine where the cuticle is modified. The perikarya of the sensory cells, a large supporting cell with a complicated surface and a second type of receptor, form a bud-like structure and are surrounded by a layer of collagen fibrils. The second receptor cell bears apical stereocilia as well as a kinocilium which are directed towards the centre of the animal — thus the cell appears to be turned upside down. The sensilla of the antennae are 1) sensory bristles containing two or three kinds of receptor cells, one of which bears an apical cilium and one kind of supportive cell and 2) sensory bulbs located within furrows consisting of receptor cells with branched cilia and two kinds of supportive cells which are covered by a modified thin cuticle. According to the electron microscopical findings the sensory spines on the lips are presumably chemoreceptors. The sensory bristles on the antennae can be regarded as mechanoreceptors and the sensory bulbs as chemoreceptors.Supported by the Deutsche Forschungsgemeinschaft (Sto 75/3)     

Ultrastructural investigations of three taxonomic characters in the trunk region of Echinoderes capitatus (Kinorhyncha, Cyclorhagida)

The classification of Kinorhyncha is mainly based upon cuticular differentiations including closing apparatus, trunk cuticle, and various appendages. This paper investigates whether ultrastructural characters support taxonomic results based upon light microscopical characters. The trunk region of Eckinoderes cupitatus bears several epidermal glands and setae and one middorsal spine on the 6th zonite. These characters are constant in number and distribution. The epidermal glands are unicellular, merocrine, glandular cells with an opening built up by several ramified canals terminating in pores within a slightly elevated ring-like bulge. Setae are composed of two cells, one merocrine glandular cell and one sensory cell with microvilli surrounding the outlet differentiation of the glandular cell. The setae have a pore on its tip, where the secretory product is released. The middorsal spine bears a multiciliar sensory cell. No pore is developed on the tip of the spine.     

Scanning electron microscopic studies of cilia

Summary A simple method for the preparation of ciliated epithelia for study with the scanning electron microscope is described. Ciliary groups are well preserved and it is possible to discern individual cilia and work out their numbers and orientation. Following scanning electron microscopical study some of the material was prepared for transmission electron microscopy and the ultrastructure of the tissue was found to be surprisingly well preserved. The tracheal epithelium of the rabbit, the olfactory epithelia of the goldfish and the rabbit, and the sensory epithelia in the statocyst of a cephalopod mollusc were examined with the scanning electron microscope to demonstrate the possibilities of the method. Acknowledgements. We would like to thank Professor J. Z. Young for his continued interest and support. The scanning electron microscope was purchased with a grant provided by the Science Research Council to Dr. Boyde, Mr. R. Willis helped in the initial stages of the study, Mr. G. Savage provided help with the goldfish material, Mr. S. Waterman provided much photographic assistance, and Mrs. N. Finney the secretarial assistance.     

Study on pathway and characteristics of ion secretion of salt glands of Limonium bicolor

Recretohalophytes with specialized salt-secreting structures, including salt glands and salt bladders, can secrete excess salts from plant tissues and enhance salinity tolerance of plants. However, the pathway and property of salt secretion by the salt gland has not been elucidated. In the article, Limonium bicolor Kuntze was used to investigate the pathway and characteristics of salt secretion of salt gland. Scanning electron microscope micrographs showed that each of the secretory cells had a pore in the center of the cuticle, and the rice grain-like secretions were observed above the pore. The chemical composition of secretions from secretory pores was mainly NaCl using environmental scanning electron microscope technique. Non-invasive micro-test technology was used to directly measure ion secretion rate of salt gland, and secretion rates of Na⁺ and Cl^? were greatly enhanced by a 200-mmol/L NaCl treatment. However, epidermal cells and stoma showed little secretion of ions. In conclusion, our results provide evidence that the salt glands of L. bicolor have four secretory pores and that NaCl is secreted through these pores of salt gland.     

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.     

The wax glands and wax secretion of Matsucoccus matsumurae at different development stages

In this paper, the wax secretions and wax glands of Matsucoccus matsumurae (Kuwana) at different instars were investigated using light microscopy, scanning electron microscopy and transmission electron microscopy. The first and second instar nymphs were found to secrete wax filaments via the wax glands located in the atrium of the abdominal spiracles, which have a center open and a series of outer ring pores. The wax gland of the abdominal spiracle possesses a large central wax reservoir and several wax-secreting cells. Third-instar male nymphs secreted long and translucent wax filaments from monolocular, biolocular, trilocular and quadrilocular pores to form twine into cocoons. The adult male secreted long and straight wax filaments in bundles from a group of 18–19 wax-secreting tubular ducts on the abdominal segment VII. Each tube duct contained five or six wax pores. The adult female has dorsal cicatrices distributed in rows, many biolocular tubular ducts and multilocular disc pores with 8–12 loculi secreting wax filaments that form the egg sac, and a rare type wax pores with 10 loculi secreting 10 straight, hollow wax filaments. The ultrastructure and cytological characteristics of the wax glands include wax-secreting cells with a large nucleus, multiple mitochondria and several rough endoplasmic reticulum. The functions of the wax glands and wax secretions are discussed.     

The fine structure of the compound sense organs on the cirri of Nereis diversicolor

Summary A study of the fine structure of the sense organs on the prostomial cirri and palps of Nereis diversicolor shows them to consist of two types of cell. There are between 7 and 15 sensory cells and a similar number of associated cells which contain many osmiophilic granules. The cell bodies of both are sub-epidermal, having a long distal process which reaches the surface in a raised sensory hillock. The sensory cells carry a cilium, which passes through the cuticle and emerges surrounded by a sheath formed from the outer layers of the epicuticle. Scanning electron micrographs show the surface of the cirrus to be covered by hair-like epicuticular microvilli, through which the sheathed cilia protrude. There is also a second type of sensory cell which occurs singly between the epithelial cells. The distal membrane of this cell is formed into a tuft of approximately 55 large microvilli which open through a pore in the epicuticle. It is suggested by their position and structure, that both these receptors resemble chemoreceptors.We should like to acknowledge the advice and technical help of Dr. J. A. Nott of the N.E.R.C. unit of Electron Microscopy, Menai Bridge, and Dr. P. E. Secker of the School of Electronic Engineering for use of the Cambridge Stereoscan. The work is supported by a grant from the Science Research Council to D.A.D.     

The fine structural organization of sternal glands of pseudergates and workers in termites (Isoptera): a comparative survey

Thirty-nine species belonging to different families of termites are studied to give a comprehensive view of the evolution of the sternal glands. Several modifications occurring at cuticular and cytological levels are described in neuter castes. The outer epicuticle is always pierced by epicuticular pores. In advanced termites the epicuticular filaments greatly increase in number and length creating a thick layer. The pore canals gradually enlarge while the cuticle changes into a lattice structure lining an extracellular space in which the secretion is stored. Two classes of cells are present in basal termites (Mastotermitidae, Hodotermitidae, Termopsidae and Kalotermitidae) but their glandular structures greatly differ between families. A more complex organization with three classes of cells is found in the Serritermitidae and Rhinotermitidae. A regressive evolution occurs in the Termitidae where only two classes of cells are present. A dual nervous control (campaniform sensilla and neurosecretory fibers) is found in lower termites, except for the Hodotermitidae which have mechanosensory bristles. In the other families, neurosecretory fibers are lacking. A comparison with phylogenetic data is given. A more versatile role of sternal glands in neuter castes is hypothesized.     

Structure of the prostomial appendages and the central nervous system in the Protodrilida (Polychaeta)

Summary The prostomial appendages and the central nervous system have been investigated by electron microscopy in Protodriloides chaetifer, P. symbioticus, Protodrilus haurakiensis, P. oculifer, P. ciliatus, P. helgolandicus, P. adhaerens, Saccocirrus krusadensis and S. papillocereus. The tentacles are highly developed, mobile sensory structures and consist of cuticle, epidermis, a different number of intraepithelial nerves, a small blind-ending blood vessel and a bundle of longitudinal muscle fibres. An internal canal is only present in Protodrilus and Saccocirrus species. On the tentacles seven types of sensory cells have been found including different multiciliated and uniciliated sensory cells with cilia penetrating the cuticle, sensory cells with non-penetrative cilia, phaosomes and basal ciliated sensory cells. The latter are described for the first time in polychaetes. From the specific pattern of innervation by up to five nerves originating close to the brain from the dorsal and ventral roots of the circumoesophageal connectives it is evident that the prostomial appendages represent palps. In the palps the nerve fibres form neuroneuronal, myoneuronal and epithelioneuronal synapses. The brain also gives rise to the stomatogastric nerves and various dorsal nerves. The palp canals are separated from the surrounding tissue by a prominent extracellular matrix. The wall is formed by muscle cells. The centre is usually completely filled with the cell bodies of these muscle fibres and large coelenchyme-like cells. These cells move freely in the canals and they are very likely the structural basis for the hydroskeletal function of the canals. The canals are completely separated from other body cavities and fluid is probably driven into the canals from the blood vascular system via podocytes located in a specific zone in the prostomium. In particular, the structure of the central nervous system with its nerves, the pattern of innervation of the palps and the palp canal system are compared with those of other polychaetes with special emphasis to the Spionida, the taxon presumed to include the sister group of the Protodrilida.     

Fine structure of the female sex pheromone-producing glands in Sesamia nonagrioides lef. (Lepidoptera : Noctuidae)

The morphology and cytology of the female sex pheromone-producing glands of Sesamia nonagrioides (Lepidoptera : Noctuidae) consist of modified intersegmental membranes; they are unusual compared with those described in other moths. There are 2 different glandular areas (a ventral area, GI, around the ostium bursae and a ring-shaped area, GII, around the ovipositor), instead of a single area (between segments 8 and 9 + 10) as in most other species. Ultrastructural features, such as developed basal invaginations and dilated intercellular spaces indicate transport of material from the hemolymph to the glandular cells, while the presence of abundant mitochondria, numerous free ribosomes, rough endoplasmic reticulum, and inclusions reveal high cellular activity. The smooth endoplasmic reticulum is absent in S. nonagrioides, in contrast to its extensive development in glands producing similar compounds in other moths. The cuticle, abnormally thick (7–8 times thicker than the glandular epithelium), is traversed by dilated pore canals forming cuticular gaps, connected with epicuticular canals. This system allows the storage and the passage of pheromone in and through the cuticle.