Coming apart at the seams: morphological evidence for pregnathal head capsule borders in adult <Emphasis Type="Italic">Tribolium castaneum</Emphasis>

Cephalization and seamless fusion of the anterior body segments during development obscure the segmental boundaries of the insect head. Most of the visible seams are thought to reflect cuticular infolding for structural reinforcement rather than a merger of cuticular plate borders. Incomplete fusions and other modifications of the adult head found in eight Tribolium mutations indicate that the frontal and gular sutures likely are true sutures that mark borders between adjacent cuticular plates, and suggest that the anterior facial shelf is a composite of three independent cuticular surfaces: ocular, antennal, and clypeo-labral. Additionally, midline splits of the clypeo-labrum and gula, and membranous lesions on the lateral head capsule reveal probable borders of adjacent cuticular plates where visible sutures are normally absent. The anterior lateral lesions seen in the Lucifer mutation mark a border between ocular and antennal plates and appear to identify part of the postfrontal sutures. While revealing or clarifying possible intersegmental borders between ocular, antennal, and clypeo-labral plates, the various modified or unfused surfaces of the head neither reveal an additional acronal plate nor support the view that the clypeo-labrum is segmentally associated with ocular cuticle.     

Fine structure of the chelicera in the spider Nephila clavata

The fine structural characteristics of the biting apparatus in the orb‐web spider Nephila clavata were studied using scanning electron microscopy. The main biting apparatuses of spiders are the chelicerae and cheliceral fangs in the cephalothorax. The chelicera of N. clavata is that of the jack‐knife (folding knife) type, which is composed of two segments, and has a labidognathous form that moves at right angles to the body axis. Each chelicera bears a hinged fang that folds into a cheliceral groove. The tips of the fangs are quite sharp, and the spider's body is well adapted to driving the fangs into prey. Just below the fang, each side of the cheliceral groove is covered with a total of seven cuticular teeth (four promarginal teeth and three retromarginal teeth) in two rows. The cheliceral fang has a single aperture at the tip of the posterior surface, and the lower margin of the fang which meets the promarginal teeth is a saw‐like groove. Fine structural observation reveals that each fang has a single venom pore, and each cuticular depressive area on the cheliceral groove has two different types of surface pit. Approximately 40 to 50 spiky protrusions were counted at the cheliceral groove, to hold prey tightly.     

A new genus of hard ticks in Cretaceous Burmese amber (Acari: Ixodida: Ixodidae)

A hard tick larva in Cretaceous Burmese amber is described as Cornupalpatum burmanicum n. g., n. sp. Diagnostic characters include a subcircular body with a marginal groove, 11 festoons, elongate four-segmented palpi with the fourth segment distinct and apical, the absence of an anal groove and eyes, and the presence of claws on palpal segment 3. The last character is unique for all members of the Ixodida, both fossil and extant. Aside from the palpal claws and marginal groove, features of the tick larva closely resemble those of members of the genus Aponomma Neumann 1899, considered one of the most primitive tick lineages today, whose hosts are primarily reptiles.     

Impact of body melanisation on contrasting levels of desiccation resistance in a circumtropical and a generalist <Emphasis Type="Italic">Drosophila</Emphasis> species

We investigated the role of cuticular lipids, body melanisation and body size in conferring contrasting levels of desiccation resistance in latitudinal populations of Drosophila melanogaster and Drosophila ananassae on the Indian subcontinent. Contrary to the well known role of cuticular lipids in water proofing in diverse insect taxa, there is lack of geographical variations in the amount of cuticular lipids per fly in both the species. In D. ananassae, quite low levels of body melanisation are correlated with lower desiccation resistance. By contrast, increased levels of desiccation resistance are correlated with quite high melanisation in D. melanogaster. Thus, species specific cuticular melanisation patterns are significantly correlated with varying levels of desiccation resistance within as well as between populations and across species. Role of body melanisation in desiccation resistance is further supported by the fact that assorted dark and light flies differ significantly in cuticular water loss, hemolymph and dehydration tolerance. However, similar patterns of body size variation do not account for contrasting levels of desiccation resistance in these two Drosophila species. Climatic selection is evidenced by multiple regression analysis with seasonal amplitude of thermal and humidity changes (Tcv and RHcv) along latitude on the Indian subcontinent. Finally, the contrasting levels of species specific distribution patterns are negatively correlated with RHcv of sites of origin of populations i.e. a steeper negative slope for D. ananassae corresponds with its desiccation sensitivity as compared with D. melanogaster. Thus, evolutionary changes in body melanisation impact desiccation resistance potential as well as distribution patterns of these two Drosophila species on the Indian subcontinent.     

Fine structural observations of the pecten oculi capillaries of the chicken

Summary The pecten oculi of the domestic chicken was examined with light, scanning and transmission electron microscopy and with freeze-etching techniques. Particular attention has been given to the capillary structure. The capillaries form an extensive anastomotic network. Their endothelial cells have apical (luminal), as well as basal, longitudinally oriented microfolds. It is assumed that the formation of apical differentiations of the endothelial surface is due to haemodynamic influences. Thus, sufficient surface area for membrane bound enzymes is achieved. These enzymes are necessary for active transcellular transport processes that require energy. In freeze-etched material, two different structures of the membrane surface of microfolds can be recognized. These results are discussed in relation to transport functions through capillary endothelial cells of the pecten. It is assumed that the pecten plays an important role in the nourishment of the retina and vitreous body. This paper was presented in part at the inaugural session of the European Club for Ophthalmic Fine Structure in Essen on January 20 and 21, 1973.     

Divergence of water balance mechanisms in two melanic Drosophila species from the western Himalayas

Drosophila busckii is more abundant under colder and drier montane habitats in the western Himalayas as compared to Drosophila melanogaster but the mechanistic basis of such climatic adaptations is largely unknown. We tested the hypothesis whether genetic variation or phenotypic plasticity of cuticular traits confer adaptive protection against desiccation stress in two melanic Drosophila species living under drier montane localities. For D. melanogaster, changes in melanisation are known to be associated with reduced water loss but there are no data on D. busckii. We investigated changes in body melanisation, cuticular lipids, desiccation resistance, water loss, extractable hemolymph volume (%), and dehydration tolerance in six sympatric populations of D. busckii and D. melanogaster over an altitudinal range of 640-2236 m. D. busckii is a melanic species but changes in cuticular water loss are negatively correlated with cuticular lipid mass and not with body melanisation. In D. melanogaster, there are no plastic effects (14-28 °C) for cuticular lipid mass but variation in body melanisation is associated with desiccation-related traits. Effects of organic solvents (hexane or chloroform: methanol), developmental plasticity and seasonal variation in cuticular lipids affect body water loss in D. busckii but no such changes occur in D. melanogaster. Thus, sympatric populations of D. busckii and D. melanogaster have evolved different water balance mechanisms under shared environmental conditions in the western Himalayas. Multiple measures of desiccation resistance in these species show clinal variation with altitude, consistent with adaptation to increased desiccation stress.     

Post-natal maturation of the retina in the albino rat. I. The pigment epithelium

The Authors studied the postnatal development of the retinal pigment epithelium in the albino rat, in order to elucidate its morphological and functional evolution, correlated to the numerous functional roles played in Vertebrates (Scheme 1). At birth, epithelial cells show few cytoplasmic organules and the apical surface provided of small depressions. From the third to the fifth postnatal day the first apical microfolds surround the depressions. From the seventh to the ninth day inner segments develop, whilst the apical surface of the epithelial cells is covered by many finger-like microfolds. During the eleventh postnatal day the buds of the outer segments and many lamellar microfolds can be demonstrated. During the sixteenth day the retina reaches its adult morphology. It is therefore well-evident that birth, similarly to many other Vertebrates, is not the last step, but only a moment, in the development of the retina: this process is completed only during postnatal life, when environmental light is able to stimulate every ocular structure.     

The sternal pore areas of geophilomorph centipedes (Chilopoda: Geophilomorpha)

Most geophilomorph centipedes have segmental clusters of exocrine glands whose opening pores are arranged in more or less well-defined sternal pore areas. We describe here the cuticular structures forming and/or accompanying the gland openings on the sternites and the shape of the pore areas along the body axis in representatives of most geophilomorph families. The cuticular ring around the pore may exhibit either of two forms. In Himantariidae ( Himantarium ) and in Dignathodontidae ( Henia ) the ring looks like a continuous ribbon with a visible suture, whereas in the representatives of the remaining families no suture is seen. As to the distribution of the pores on ventral surface of the body, we record the presence of pores on the last leg-bearing segment of Clinopodes flavidus , whereas that segment was described as poreless in all geophilomorphs. We also provide a taxonomic survey of shape and distribution of pore areas in the individual families, where the pore areas may take very different shapes that we regard as transformational homologues. As for the segmental distribution of sternal pore areas, there is a considerable amount of complexity along the trunk of geophilomorph centipedes, in contrast to the apparently uniform trunk structure.     

Ultrastructure of Lamblia duodenalis. I. Body Surface, Sucking Disc and Median Bodies

SYNOPSIS. The body surface, sucking disc and median bodies of Lamblia duodenalis have been studied on ultrathin sections in the electron microscope. The body is covered by a pellicle, displaying a striated structure in the area of the sucking disc. The striation is due to 150 Å thick dense ridges which are spaced in distances of 200–400 Å. The ridges are formed by the internal pellicular membrane and have a triangular cross section with a very dense apex. They are arranged concentrically and run parallel to the surface of the sucking disc lobes. Anteriad to the nuclei in the median line a space is free of ridges. The margin of the sucker is elevated above the body forming a sharp crest of the ridged pellicle.
This crest is the inner wall of a marginal groove delimiting the sucker from the body. The outer margin is circumscribed by a fold in the body tapering to the posterior end. A ventral groove containing the two ventral flagella lies in the median line. The movement of the ventral flagella pushes the medium through the marginal and ventral grooves thus producing vacuum in the sucker area.
The median bodies are composed of numerous 150 Å thick tubular fibrils. They differ in their ultrastructure from the parabasal apparatus in other flagellates and have nothing in common with the kinetoplasts. Their functional significance awaits elucidation.     

The cuticle of the Aplacophora and its evolutionary significance in the Mollusca

The cuticle of Proneomenia consists of a mucoid matrix containing calcareous spicules and is secreted by the mantle epithelium at the base of the ventral (pedal) groove and over the general body surface. Histochemical examination shows the matrix to be composed of a glycoprotein complex with high acid mucopolysaccharide and low protein contents in which tanning plays little part in stabilization.
The cuticle of the Aplacophora is tentatively equated with an early mucoid stage in the evolution of the molluscan shell and it is suggested that secretion of additional protein, followed by hardening by quinone-tanning, are necessary further stages before a calcified shell evolves. The aplacophoran cuticle is compared with that of Acanthochitona (Polyplacophora) and, although they are similar in many respects, the latter has in addition a discrete inner cuticular layer whichmay act as a semi-conducting membrane in the deposition of the calcareous plates. The spicules are similar in both groups, each being secreted within a thin cup-like membrane which exhibits somewhat similar properties to the inner cuticle.     

Changes in cuticular lipids, water loss and desiccation resistance in a tropical drosophilid: analysis of variation between and within populations

We investigated within as well as between population variability in desiccation resistance, cuticular lipid mass per fly and cuticular water loss in nine geographical populations of a tropical drosophilid, Zaprionus indianus. Interestingly, the amount of cuticular lipids and desiccation resistance in this non-melanic species are significantly higher as compared with melanic Drosophila melanogaster. On the basis of isofemale line analysis, within population trait variability in cuticular lipid mass per fly is positively correlated with desiccation resistance and negatively correlated with cuticular water loss but show lack of correlation with body size. We observed geographical variation in the amount of cuticular lipid mass per fly in Zaprionus indianus but no such divergence was found in D.melanogaster. In both the species, geographical variations in desiccation resistance are negatively correlated with cuticular water loss but the underlying mechanisms for changes in cuticular permeability are quite different. Thus, we may suggest that body melanisation and cuticular lipids may represent alternative strategies for coping with dehydration stress in melanic versus non-melanic drosophilids. For both the species, desiccation resistance and cuticular water loss are correlated with regular increase in aridity in the northern subtropical localities as compared with southern peninsular humid tropical localities. The role of climatic selection is evident from multiple regression analysis with seasonal changes in temperature and humidity (Tcv and RHcv) of the sites of origin of populations of Zaprionus indianus along latitude.     

Rearrangement of enveloping layer cells without disruption of the epithelial permeability barrier as a factor in Fundulus epiboly

Silver nitrate staining of blastoderms of Fundulus heteroclitus gastrulae shows that the number of marginal cells of the enveloping layer (EVL) is reduced from 160 to 25 during epiboly. To determine whether this decrease in the number of marginal cells was due to ingression, cell death, or rearrangement of cells, marginal and submarginal regions of the late gastrula were observed directly by time-lapse cinemicrography. Marginal cells rearrange to occupy submarginal positions by first narrowing their boundary with the external yolk syncytial layer (E-YSL), thus becoming tapered in shape. Then, the narrowed marginal boundary retracts from the E-YSL and moves submarginally in the plane of the epithelium. Concurrently, the marginal cells on both sides come into apposition; no gap or break appears in the circum-apical continuity of the epithelial sheet. Marginal cells leave the margin of the EVL during epiboly at a rate of about six per hour. The rate of movement of the EVL cells with respect to one another is about 0.5 to 1.0 micron/min at 21 degrees C. Submarginal cells rearrange in a similar fashion. Although no protrusive activity was seen at the lateral aspects of rearranging cells, the tapering or narrowing associated with rearrangement was accompanied by formation of microfolds on their apical surfaces, and separating or recently separated submarginal cells form "flowers" of microfolds on their apices adjacent to the site of separation. Morphometric analysis shows that about half the narrowing of the margin of the EVL during epiboly is accounted for by cell rearrangement and the other half by the associated tapering and narrowing. These results suggest that epiboly of the EVL may have an active component as well as a passive one.     

Fine structure of the conus papillaris in the bobtail goanna (Tiliqua rugosa)

The structure of the conus papillaris in an Australian lizard, the bobtail goanna (Tiliqua rugosa) was investigated by light and electron microscopy. In this strongly diurnal species, the conus papillaris consists of a heavily vascularized and pigmented, finger-like structure about 1 mm in diameter and 3-4 mm in length. It is situated over the optic nerve head and projects into the vitreous chamber. Within the conus are numerous capillaries and larger blood vessels, melanocytes and occasional mast cells. Many of the capillaries display prominent luminal and abluminal microfolds. Other capillaries show no microfolds while still others display an intermediate number of microfolds. The larger blood vessels are usually indistinguishable as to being either arterioles or venules. The endothelial cells of all blood vessels show a population of cytoplasmic granules. The melanocytes are large pleomorphic cells usually rich in microfilaments. Unmyelinated nerve processes are plentiful within the conus and the Schwann cells enclosing these nerve fibres are occasionally seen to be pigmented. The morphology of the conus papillaris indicates a heavy involvement in the transport of materials. It is considered to be homologous to the pecten oculi of the avian eye; to the falciform process of the teleost eye; to the supraretinal vessels of amphibians and to the intraretinal vessels of the mammalian eye.     

Fungistatic activity of the sternal gland secretion of the dampwood termite <Emphasis Type="Italic">Zootermopsis angusticollis</Emphasis>

Summary In vivo and in vitro studies indicate that cuticular chemicals from the ventral region of the abdomen where the sternal gland of the dampwood termite Zootermopsis angusticollis is located have fungistatic properties. Germination rates of conidia of the entomopathogenic fungus Metarhizium anisopliae were significantly reduced from 91% (controls) to 38.5% after nymphs walked over conidia-seeded agar medium, but did not differ from controls when the sternal gland and surrounding cuticle were sealed with nail polish. In vitro studies show that germination of fungal conidia was also significantly reduced following incubation with cuticular extracts of either sternal or tergal segments suggesting that cuticular exudates in general may have antifungal properties. Extracts of sternites had greater fungistatic activity than extracts of tergites, but the difference was not statistically significant. Extracts of the sternal gland significantly reduced germination rates by up to 9%. Germination rates were significantly reduced when conidia were incubated with n-hexanoic acid, or its vapor. n-Hexanoic acid has been recovered from whole body extracts of Zootermopsis nevadensis and may indeed be a component of the sternal gland of Z. angusticollis. Here we suggest that sternal gland secretions in termites may have had the original function of controlling microbes within the nest and their prominent role in communication may have evolved secondarily.Received 18 April 2003; revised 20 November and 17 December 2003; accepted 19 January 2004.     

Sexual dimorphism for water balance mechanisms in montane populations of Drosophila kikkawai

Conservation of water is critical to the ecological success of Drosophila species living in the drier montane localities of the Western Himalayas. We observed clinal variation in desiccation resistance for both sexes of Drosophila kikkawai from an altitudinal transect (512–2226 m above sea level). Since more than 90 per cent of body water is lost through cuticular transpiration, the target of selection may be cuticular lipids or cuticular melanization. We tested whether melanic females and non-melanic males of D. kikkawai have similar mechanisms of desiccation resistance. There is clinal variation in the amount of cuticular lipids per fly in males, but not in females. By contrast, for females, elevational increase in melanization is positively correlated with desiccation resistance and negatively with cuticular water loss, but there is no variation in the amount of cuticular lipids. Thus, sexual dimorphism for the mechanism of desiccation resistance in D. kikkawai matches the water proofing role of body melanization as well as cuticular lipids.     

Organization of the spinnerets and spigots in the orb web spider,Argiope bruennichi (Araneae: Araneidae)

Although the basic taxonomic characteristics usually remain unchanged, some spinning apparatuses undergo consistent adaptive variations. As the presence of additional protuberances known as nubbins and tartipores have caused disagreements regarding some Araneidae spiders, more detailed definitions on the cuticular structures have recently been proposed. Reflecting this definition, microstructural organization of silk spinning apparatuses in the orb web spider Argiope bruennichi were reconsidered using field emission scanning electron microscopy. Among the seven kinds of functional spigots in females, it was revealed that two types (major ampullates and pyrifoms) are located on anterior spinnerets and another five types are distributed on median (minor ampullates, tubuliforms and aciniforms) or posterior (tubuliforms, flagelliforms, aggregates and aciniforms) spinnerets, respectively. In addition to functional spigots, cuticular remnants of the nubbins and the tartipores were found on the spinning fields, but the number of tartipores on each spinneret varied among individuals based on maturity. Nevertheless, three kinds of cuticular protuberances of ampullate silk glands were clearly visible at both the anterior and median spinnerets.     

Impact of body melanisation on desiccation resistance in montane populations of D. melanogaster: Analysis of seasonal variation

In the montane localities of subtropical regions, winter is the dry season and ectothermic drosophilids are expected to evolve desiccation resistance to cope with drier climatic conditions. An analysis of six montane populations (600–2226 m) of D. melanogaster showed variations for body melanisation (i.e. pigmentation) and desiccation resistance across seasons as well as along altitude. During winter season, plastic changes for melanisation of three posterior abdominal segments (5th + 6th + 7th) correspond with higher desiccation resistance. Thus, we analyzed genetic and plastic effects for these ecophysiological traits by comparing wild-caught and laboratory reared individuals of D. melanogaster for autumn as well as winter season. A ratio of slope values in wild vs. laboratory populations has shown a 1.64-fold plastic effect during autumn; and a two-fold effect during winter. For body melanisation and desiccation resistance, evolutionary response to altitudinal environmental gradient is similar to the phenotypic response across seasons. Thus, our observations are in agreement with the co-gradient hypothesis. Further, we tested the hypothesis whether a thicker cuticle (either due to melanisation or cuticular lipids) leads to lesser cuticular water loss and higher desiccation resistance across seasons as well as according to altitude. Based on within and between population analyses, body melanisation was found to be positively correlated with desiccation resistance but negatively with cuticular water loss. Interestingly, there were no changes in the amount of cuticular lipids per fly across seasons as well as along altitude; and therefore cuticular lipids did not account for desiccation resistance. Cuticular water loss exhibited negative correlation with body melanisation but not with cuticular lipids as well as with changes in body size across seasons. Thus, our data suggest that seasonal changes in body melanisation confer desiccation resistance in montane populations of D. melanogaster.     

Direct attachment of eggs to the body wall in the externally brooding sea anemone <Emphasis Type="Italic">Cnidopus japonicus</Emphasis> (Actiniaria; Actiniidae)

The externally brooding sea anemone Cnidopus japonicus (Verrill) inhabits boulder shores between the mid-intertidal and shallow subtidal zones of Mutsu Bay, northern Japan. The anemones usually adhere to the side and under-surfaces of boulders. These anemones keep offspring on the middle part of their body wall during the breeding season. Our observations of spawning behavior in an aquarium revealed that this anemone lays eggs through an elongated oral margin and directly attaches the eggs to its body wall, while making a circular groove on the column. The anemone rotates its elongated oral margin around its body trunk several times and arranges eggs in the circular brooding groove. This behavior suggests that mother anemones, regardless of their attachment position on substrata, are able to attach their offspring effectively to their body wall. Electronic Publication     

Fine structure of the Gene's organ in the camel tick Hyalomma (Hyalomma) dromedarii (Ixodoidea: Ixodidae)

Gene's organ of the camel tick Hyalomma (Hyalomma) dromedarii is located in the anterodorsal region of the body cavity ventrad to the scutum. It consists of a short stalk, dividing posteriorly into 2 pairs of horns and then into tubular glands. In unfed ticks, the epithelial layer of both the stalk and horns is lined internally by 2 cuticular layers; an inner, thin, greatly folded, dense layer surrounds the organ main lumen, and an outer, thick, slightly folded, less dense layer abuts the cell apices. Only the inner cuticular layer extends into the horn posterior region and appears perforated with numerous pore canals and covered with fine, cuticular projections. The horn and tubular glands epithelium is structurally consistent with a secretory function that apparently increases as feeding progresses. During oviposition, the inner cuticular layer unfolds and inflates into a pair of balloonlike structures that evert through the organ external aperture to receive and manipulate each egg as it is laid, coating it with a waxy layer that prevents desiccation. The fine cuticular projections may have a function in gripping the eggs as they leave the vagina. This organ appears to be everted by hydrostatic pressure from the hemolymph and is retracted by muscles.