Elaboration and ultrastructural changes in the pore canal system of the mineralized cuticle of Carcinus maenas during the moulting cycle

Two basic structural components are concerned in the elaboration of the pore canal system in the mineralized cuticle of the decapod crab Carcinus maenas: tubular cytoplasmic extensions originating from epidermis and vertical fibres. These components are present from the moment the first procuticular materials of the new cuticle are laid down but their organization varies according to a precise schedule during the further moult cycle stages. Cytoplasmic extensions form a complicated branching system connecting the epidermal layer with all regions of the cullcular compartment, at least transitorily. During the moult cycle the prolongation of this cellular system appears to result from two concomitant but opposite phenomena. Before ecdysis the growth of cell extensions in the proximal cuticular layers prevails over their regression at the distal level. During the post-moult period these phenomena are reversed in importance so that the pore canal system is without cytoplasmic material as soon as intermoult starts. The depositing of vertical fibres takes place in close contact with the proximal cell extension plasma membrane, which never bears dense plaques. As moult stages progress, they are gradually organized into twisted sheaths that persist throughout the intermoult. Incidentally, some fibres invade the pore canal lumen freed from cell extensions. Some aspects regarding the fine organization, the chemical composition and the functional significance of both epidermal tubular extensions or vertical fibres are also discussed in the light of previous investigations carried out on crustaceans and in other arthropods.     

Ultrastructural diversity in the pore canal systems of amphipod crustaceans

Transmission electron microscopy was used to analyze the structure and organization of the intracuticular pore canal system in 34 species of amphipod crustaceans. Pore canals were detectable in all species, including those that, from scanning electron microscopy, had been considered to lack them. Canal structure ranges from simple transcuticular passages of uniform diameter to more elaborate systems with distal canal dilatations variously equipped with electron dense collars, tubular filaments, single or multiple channels leading to the surface and transverse partitions separating canal contents of different electron densities. Considerable branching between tubular elements of the canal system is evident in many species. In most species the canals communicate with the outsidevia epicuticular channels. Even in those species in which this communication was not established, their epicuticle generally contains abundant cavities with external pores. Although some consistency in structure and organization is present among a few groups of taxonomically related species, pore canal characteristics generally could not be correlated with habitat or life style. It is suggested that the structural and organizational variety present reflects a considerable array of functions among amphipod pore canal systems.     

The membranous labyrinth and its innervation inChaetodon trifasciatus (Pisces,Teleostei, Chaetodontidae)

Synopsis In the butterflyfishChaetodon trifasciatus, the labyrinth is characterized by its elevated form and especially the size of the vertical canals, the almost circular form of the horizontal canal and its posterior opening not directly in the utriculus but in the common pillar of the two vertical canals. There is an almost complete separation between utriculus and sacculus which are only linked by a virtual pore. The lagena, which is medially situated to the posterior part of the sacculus, is separated from it by an incomplete vertical wall. There are two maculae neglectae, the anterior macula being situated in the pore separating utriculus from sacculus and filling this pore, the posterior in a gutter of the floor of the utriculus. A long and narrow endolymphatic canal, originating from the sacculus close to the communication with the utriculus, follows the common pillar of the two vertical canals and widens into an endolymphatic sac at the top of the membranous labyrinth. The innervation of the labyrinth is made by the acoustic ganglion, which is connected to the brain by two roots and elongated into three parts: the anterior part innervates the anterior and horizontal cristae and the utricular and saccular maculae; the middle part innervates the macula sacculae and the macula neglecta 1; the posterior part innervates the macula neglecta II, the macula lagenae and the posterior crista. The important size of the vertical canals and the almost circular form of the horizontal canal may reflect very precise locomotory aptitudes.     

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.     

Development and ultrastructure of the rigid dorsal and flexible ventral cuticles of the elytron of the red flour beetle,Tribolium castaneum

Insect exoskeletons are composed of the cuticle, a biomaterial primarily formed from the linear and relatively rigid polysaccharide, chitin, and structural proteins. This extracellular material serves both as a skin and skeleton, protecting insects from environmental stresses and mechanical damage. Despite its rather limited compositional palette, cuticles in different anatomical regions or developmental stages exhibit remarkably diverse physicochemical and mechanical properties because of differences in chemical composition, molecular interactions and morphological architecture of the various layers and sublayers throughout the cuticle including the envelope, epicuticle and procuticle (exocuticle and endocuticle). Even though the ultrastructure of the arthropod cuticle has been studied rather extensively, its temporal developmental pattern, in particular, the synchronous development of the functional layers in different cuticles during a molt, is not well understood. The beetle elytron, which is a highly modified and sclerotized forewing, offers excellent advantages for such a study because it can be easily isolated at precise time points during development. In this study, we describe the morphogenesis of the dorsal and ventral cuticles of the elytron of the red flour beetle, Tribolium castaneum, during the period from the 0 d-old pupa to the 9 d-old adult. The deposition of exocuticle and mesocuticle is substantially different in the two cuticles. The dorsal cuticle is four-fold thicker than the ventral. Unlike the ventral cuticle, the dorsal contains a thicker exocuticle consisting of a large number of horizontal laminae and vertical pore canals with pore canal fibers and rib-like veins and bristles as well as a mesocuticle, lying right above the enodcuticle. The degree of sclerotization appears to be much greater in the dorsal cuticle. All of these differences result in a relatively thick and tanned rigid dorsal cuticle and a much thinner and less pigmented membrane-like ventral cuticle.     

The Structure and Mineralization of the Carapace of the Crab (Cancer pagurus L.) 2. The exocuticle

The exocuticle of the dorsal carapace of the intermoult Cancer pagurus was studied by means of light microscopy, electron microscopy, and contact microradiography. In the exocuticle a 5-15 μm wide highly mineralized external zone was seen where prisms were not present. The cross-sectional shape and diameter of the prisms varied. The prisms were separated by interprismatic areas varying in width and in degree of mineralization. With increasing width of the interprismatic areas the diameter of the prisms decreased. The prism-less external zone may be the result of complete mineralization of the prisms. The pore canals of the exocuticle were circular in cross section and present both within the prisms and within the interprismatic areas. The lamellar system of the exocuticle was built up by layers of horizontal fibrils which were interconnected by vertical or oblique fibrils. The minerals of the external prism-less zone occurred as aggregates of crystalline matter or as large brick-like structures. Crystal edge lengths up to 300 nm were measured. In well mineralized interprismatic areas aggregates of crystals and relatively large crystals were observed. In poorly mineralized interprismatic areas small plate-like crystals occurred. Occasionally a prism-less zone was seen near the exocuticle/endocuticle junction.     

Ultrastructural organization of hypodermis and formation of cuticle in pharate larva of Leptotrombidium orientale (Acariformes: Trombiculidae)

The ultrastructural organization of hypodermis and the process of cuticle deposition is described for the pharate larvae of a trombiculid mite, Leptotrombidium orientale, being under the egg-shell and prelarval covering. The thin single-layered hypodermis consists of flattened epithelial cells containing oval or stretched nuclei and smooth basal plasma membrane. The apical membrane forms short scarce microvilli participating in the cuticle deposition. First of all, upper layers of the epicuticle, such as cuticulin lamella, wax and cement layers, are formed above the microvilli with plasma membrane plaques. Cuticulin layer is seen smooth at the early steps of this process. Very soon, however, epicuticle starts to be curved and forms particular high and tightly packed ridges, whereas the surface of hypodermal cells remains flat. Then a thick layer of the protein epicuticle is deposited due to secretory activity of hypodermal cells. Nearly simultaneously the thick lamellar procuticle starts to form through the deposition of their microfibrils at the tips of microvilli of the apical plasma membrane. Procuticle, as such, remains flat, is situated beneath the epicuticular ridges and contains curved pore canals. Cup-like pores in the epicuticle provide augmentation of the protein epicuticle mass due to secretion of particular substances by cells and to their transportation through the pore canals towards these epicuticular pores. The very beginning of the larval cuticle formation apparently indicates the starting point of the larval stage in ontogenesis, even though it remains for some time enveloped by the prelarval covering or sometimes by the egg-shell. When all the processes of formation are over, hungry larvae with a fully formed cuticle are actively hatched from two splitted halves of prelarval covering.     

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.     

Interrelations between auditory and vestibular receptors in the frog's labyrinth

Summary The influence of the efferent vestibular system being eliminated, the spontaneous activity of afferent fibres of the ampullary nerves of the horizontal and vertical anterior semicircular canals was recorded in the frog. By functionally eliminating either both papillae or all the vestibular receptors except for the papillae, and then using statistical methods, as well as by stimulating the papillae by sounds or the papillary nerve fibres by electrical stimulus, it has been shown that the auditory papillae have a facilitatory influence on the spontaneous afferent activity from the horizontal and vertical anterior canals. This influence is most likely mediated by receptor-receptor fibres arising from the auditory organs and innervating the semicircular canals.Abbreviations HC horizontal canal - VAC vertical anterior canal This research was supported by a grant from D.G.R.S.T. (Aide à la Recherche n 77.7.1127)     

SEM observations on the cuticles of some decapod crustaceans

The cuticles of the crayfish Austropotamobius pallipes (Lereboullet), and the crabs Cancer pagurus L. and Carcinus maenas (L.), have been examined with the scanning electron microscope. Laminae are composed of sheets of horizontal fibres which subsequently are into the inter-laminae. The inter-laminae contain sheets of fibres which are at a slight angle from the horizontal between sucessive laminae. The disposition of the pore canals is clearly related to fibre pattern. The sinuous macrofibres described by Dennell (1973) are discrete from the pore canals.     

Apple Fruit Cuticles and the Occurrence of Pores and Transcuticular Canals

Developmental studies were made on the dewaxed thin-sectionedapple fruit cuticles of 10 Malus sylvestris Mill, cultivarsfrom 4 weeks before anthesis through fruit maturation and harvest.Cuticular development appears to correlate well with the generalgrowth of the fruit. However, no correlation exists betweenfruit size and cuticle thickness. Cuticular pores were evidentas early as 1 week before anthesis and transcuticular canalsbecame evident by 1 week following anthesis. Dewaxed thin-sectioned,as well as isolated, mature fruit cuticles of 16 cultivars andfour crab-apples consistently revealed the distinct presenceof ubiquitous pores and canals. Evidence is provided by lightmicroscopy and scanning electron microscopy (SEM). Measurementswere taken of cuticle thicknesses during development and ofcuticular pore dimensions, and calculations were made of poreand canal numbers. Fruit size alone is not directly indicativeof total pore numbers per surface area. Canal lengths are directlyrelated to the developmental thickness of the cuticle. No correlationwas found between the thickness of the mature cuticle and eitherthe number of pores present or the pore diameters. Malus sylvestris Mill, apple fruit, morphology, cuticle, cuticular flanges, cuticular pores, transcuticular canals, ultrastructure     

The integumental ultrastructure of Parathalestris harpactoides (Claus, 1863) (copepoda,harpacticoida)

The integument of Parathalestris harpactoides (Claus, 1863) is studied by scanning and transmission electron microscopy. The general structure of the integument conforms to the common pattern known from Copepoda. Emphasis is given to the structural variation of the cuticle in different regions of the body. The cuticle measures about 6 µm in most parts of the body, and shows a laminate appearance. The epicuticle is about 60 nm thick. Numerous pore canals containing muscular tonofilaments penetrate the procuticular layer of the integument. A peculiar feature is the presence of a honeycombed layer in the outermost zone of the cuticle of some parts of the body. The epidermal layer, muscle insertions and integumental pores are of common type. The cuticle of some specimens, both males and females, is covered with microorganisms.     

The ultrastructure of the cuticle of some British lumbricids (Annelida)

The ultrastructure of the cuticle of 11 species of British lumbricids is described. The number of unbanded collagenous fibre layers varies with the species and is roughly proportional to the size of the adult worm. Four zones are discernible in the cuticle matrix in all species except E. foetida where the outermost zone shows subdivision.
Microvilli, cytoplasmic extensions from the epithelial surface, occur. The "long" and "short" microvilli of other workers are shown to be different views of the same structure. The microvilli have an ovoid base with the two poles forming low shoulders on either side of the ascending microvillus. The bases are oriented at right-angles to the longitudinal axis of the worm and the microvilli are arranged in regular staggered rows along the same axis. Details of the spatial alignment of the microvilli are given and the possible role of these regularly arranged structures as factors in the orientation of the collagen fibre unit filaments is discussed, and it is speculated that they might also have some proprioceptive function.
Distally the microvilli terminate among the surface epicuticular projections and are shown to give rise to them. The epicuticular projections are peanut-shell shaped with a distinct substructure consisting of a 8 nm electron dense lining and two parallel dense discs, each 8 nm deep, above the "waist".
The mucous cell pores are lined with electron pale microfibrillar material and at the base of the pore a circlet of 13–15 short microvilli, with prominent tonofilaments, arises from the cytoplasm of the mucous cell. Surrounding the pore microvilli are numerous, small, membrane bound mucous pore particles.     

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.     

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.     

The Prevalence of Pores and Canals in Leaf Cuticular Membranes

Ubiquitous, visibly discrete, natural cuticular pores and transcuticularcanals were found in the dewaxed leaf (and one herbaceous stem)cuticular membranes of 27 out of 32 taxa among 14 families.Clear evidence for their existence is provided by light photomicrographs.Both adaxial and abaxial leaf surfaces were investigated usingthin transections and chemically isolated cuticular membranes,in conjunction with ordinary staining techniques and light microscopymethods. No correlations were found between cuticle thicknessesand either the frequency of pore or the pore and canal diameters. Leaf cuticles, cuticle morphology, cuticular pores, transcuticular canals, cuticular flanges     

The fine structure of the outer surface of the incubated eggshells of the Helmeted guinea fowl (Numidia meleagris)

The surface of the eggshells of the Helmeted guinea fowl (Numidia meleagris) was polished during incubation by the parent. Examination with the light microscope showed that the cuticle had been removed from the ridges on the outer surface of the shell and that the plugs in the outer orifice of the pore canals had acquired extraneous materials including grease. Studies with a scanning electron microscope revealed that the spheres that made up the pore plugs retained their identity even though they were stained. It was concluded that ridges on the shell surface protected the pore plugs from damage by attrition and that the plugs acted as filters thereby preventing nest debris from occluding the pore canals or contaminating the shell membranes.     

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.